S-NAIL(1) User Commands S-NAIL(1)

NAME

S-nail [v14.9.25] - send and receive Internet mail

SYNOPSIS

s-nail [-DdEFinv~#] [-: spec] [-A account] [:-a attachment:]
[:-b bcc-addr:] [:-C "field: body":] [:-c cc-addr:]
[-M type | -m file | -q file | -t] [-r from-addr]
[:-S var[=value]:] [-s subject] [:-T "field: addr":] [:-X cmd:]
[:-Y cmd:] [-.] :to-addr: [-- :mta-option:]

s-nail [-DdEeHiNnRv~#] [-: spec] [-A account] [:-C "field: body":]
[-L spec] [-r from-addr] [:-S var[=value]:] [-u user] [:-X cmd:]
[:-Y cmd:] [-- :mta-option:]
s-nail [-DdEeHiNnRv~#] [-: spec] [-A account] [:-C "field: body":] -f
[-L spec] [-r from-addr] [:-S var[=value]:] [:-X cmd:]
[:-Y cmd:] [file] [-- :mta-option:]

s-nail -h | --help
s-nail -V | --version

DESCRIPTION

Note: S-nail (S-nail) will see major changes in v15.0 (circa
2022). Some backward incompatibilities cannot be avoided.
COMMANDS change to Shell-style argument quoting, and shell
metacharacters will become (more) meaningful. Some commands
accept new syntax today via wysh (Command modifiers). Behaviour
is flagged [v15-compat] and [no v15-compat], setting v15-compat
(INTERNAL VARIABLES) will choose new behaviour when applicable;
giving it a value makes wysh an implied default. [Obsolete]
flags what will vanish.

Warning! v15-compat (with value) will be a default in v14.10.0!

S-nail provides a simple and friendly environment for sending and
receiving mail. It is intended to provide the functionality of the
POSIX mailx(1) command, but is MIME capable and optionally offers
extensions for line editing, S/MIME, SMTP and POP3, among others. S-
nail divides incoming mail into its constituent messages and allows the
user to deal with them in any order. It offers many COMMANDS and
INTERNAL VARIABLES for manipulating messages and sending mail. It
provides the user simple editing capabilities to ease the composition
of outgoing messages, and increasingly powerful and reliable non-
interactive scripting capabilities.

Options

-: spec, --resource-files=..
Controls loading of (as via source) Resource files: spec
is parsed case-insensitively, the letter `s' corresponds
to the system wide s-nail.rc, `u' the user's personal file
~/:.mailrc. The (original) system wide resource is also
compiled-in, accessible via `x'. The letters `-' and `/'
disable usage of resource files. Order matters, default
is `su'. This option overrides -n.

-A name, --account=..
Activate user account name after program startup is
complete (resource files loaded, only -X commands are to
be executed), and switch to its primary system mailbox
(most likely the inbox). If activation fails the program
exits if used non-interactively, or if any of errexit or
posix are set.

-a file[=input-charset[#output-charset]], --attach=..
(Send mode) Attach file. For (Compose mode) opportunities
refer to ~@ and ~^. file is subject to tilde expansion
(see Filename transformations and folder); if it is not
accessible but contains a `=' character, anything before
the last `=' will be used as the filename, anything
thereafter as a character set specification, as shown.

If only an input character set is specified, the input
side is fixed, and no character set conversion will be
applied; an empty or the special string hyphen-minus `-'
is taken for ttycharset (the default). If an output
character set has also been specified the desired
conversion is performed immediately, not considering file
type and content, except for an empty string or hyphen-
minus `-', which select the default conversion algorithm
(see Character sets): no immediate conversion is
performed, file and its contents will be MIME-classified
(HTML mail and MIME attachments, The mime.types files)
first -- only the latter mode is available unless features
includes `,+iconv,'.

-B ([Obsolete]: S-nail will always use line-buffered output,
to gain line-buffered input even in batch mode enable
batch mode via -#.)

-b addr, --bcc=..
(Send mode) Send a blind carbon copy to recipient addr.
The option may be used multiple times. Also see the
section On sending mail, and non-interactive mode.

-C "field: body", --custom-header=..
Create a custom header which persists for an entire
session. A custom header consists of the field name
followed by a colon `:' and the field content body, for
example `-C "Blah: Neminem laede; imo omnes, quantum
potes, juva"'. Standard header field names cannot be
overwritten by custom headers. Runtime adjustable custom
headers are available via the variable customhdr, and in
(Compose mode) ~^, one of the COMMAND ESCAPES, as well as
digmsg are the most flexible and powerful options to
manage message headers. This option may be used multiple
times.

-c addr, --cc=..
(Send mode) Just like -b, except it places the argument in
the list of carbon copies.

-D, --disconnected
[Option] Startup with disconnected set.

-d, --debug Enter a debug-only sandbox mode by setting the internal
variable debug; the same can be achieved via `-S debug' or
`set debug'. Also see -v.

-E, --discard-empty-messages
(Send mode) set skipemptybody and thus discard messages
with an empty message part body, successfully.

-e, --check-and-exit
Just check if mail is present (in the system inbox or the
one specified via -f): if yes, return an exit status of
zero, a non-zero value otherwise. To restrict the set of
mails to consider in this evaluation a message
specification can be added with the option -L. Quickrun:
does not open an interactive session.

-F (Send mode) Save the message to send in a file named after
the local part of the first recipient's address (instead
of in record).

-f, --file Read in the contents of the user's secondary mailbox MBOX
(or the specified file) for processing; when S-nail is
quit, it writes undeleted messages back to this file (but
be aware of the hold option). The optional file argument
will undergo some special Filename transformations (as via
folder). Note that file is not an argument to the flag
-f, but is instead taken from the command line after
option processing has been completed. In order to use a
file that starts with a hyphen-minus, prefix with a
relative path, as in `./-hyphenbox.mbox'.

-H, --header-summary
Display a summary of headers for the given folder
(depending on -u, inbox or MAIL, or as specified via -f),
then exit. A configurable summary view is available via
the option -L. This mode does not honour showlast.
Quickrun: does not open an interactive session.

-h, --help Show a brief usage summary; use --long-help for a list
long options.

-i set ignore to ignore tty interrupt signals.

-L spec, --search=..
Display a summary of headers of all messages that match
the given spec in the folder found by the same algorithm
used by -H, then exit. See the section Specifying
messages for the format of spec. This mode does not
honour showlast.

If the -e option has been given in addition no header
summary is produced, but S-nail will instead indicate via
its exit status whether spec matched any messages (`0') or
not (`1'); note that any verbose output is suppressed in
this mode and must instead be enabled explicitly (see -v).
Quickrun: does not open an interactive session.

-M type (Send mode) Will flag standard input with the MIME
`Content-Type:' set to the given known type (HTML mail and
MIME attachments, The mime.types files) and use it as the
main message body. [v15 behaviour may differ] Using this
option will bypass processing of message-inject-head and
message-inject-tail. Also see -q, -m, -t.

-m file (Send mode) MIME classify the specified file and use it as
the main message body. [v15 behaviour may differ] Using
this option will bypass processing of message-inject-head
and message-inject-tail. Also see -q, -M, -t.

-N, --no-header-summary
inhibit the initial display of message headers when
reading mail or editing a mailbox folder by calling unset
for the internal variable header.

-n Standard flag that inhibits reading the system wide
s-nail.rc upon startup. The option -: allows more control
over the startup sequence; also see Resource files.

-q file, --quote-file=..
(Send mode) Initialize the message body with the contents
of file, which may be standard input `-' only in non-
interactive context. Also see -M, -m, -t.

-R, --read-only
Any mailbox folder aka folder opened will be in read-only
mode.

-r from-addr, --from-address=..
The RFC 5321 reverse-path used for relaying and delegating
messages to its destination(s), for example to report
delivery errors, is normally derived from the address
which appears in the from header (or, if that contains
multiple addresses, in sender). A file-based aka local
executable mta (Mail-Transfer-Agent), however, instead
uses the local identity of the initiating user.

When this command line option is used the given single
addressee from-addr will be assigned to the internal
variable from, but in addition the command line option -f
from-addr will be passed to a file-based mta whenever a
message is sent. Shall from-addr include a user name the
address components will be separated and the name part
will be passed to a file-based mta individually via -F
name. Even though not a recipient the `shquote'
expandaddr flag is supported.

If an empty string is passed as from-addr then the content
of the variable from (or, if that contains multiple
addresses, sender) will be evaluated and used for this
purpose whenever the file-based mta is contacted. By
default, without -r that is, neither -f nor -F command
line options are used when contacting a file-based MTA,
unless this automatic deduction is enforced by setting the
internal variable r-option-implicit.

Remarks: many default installations and sites disallow
overriding the local user identity like this unless either
the MTA has been configured accordingly or the user is
member of a group with special privileges. Passing an
invalid address will cause an error.

-S var[=value], --set=..
set (or, with a prefix string `no', as documented in
INTERNAL VARIABLES, unset) variable and optionally assign
value, if supported; [v15 behaviour may differ] the entire
expression is evaluated as if specified within dollar-
single-quotes (see Shell-style argument quoting) if the
internal variable v15-compat is set. If the operation
fails the program will exit if any of errexit or posix are
set. Settings established via -S cannot be changed from
within Resource files or an account switch initiated by
-A. They will become mutable again before commands
registered via -X are executed.

-s subject, --subject=..
(Send mode) Specify the subject of the message to be sent.
Newline (NL) and carriage-return (CR) bytes are invalid
and will be normalized to space (SP) characters.

-T "field: addr", --target=..
(Send mode) Add addr to the list of receivers targeted by
field, for now supported are only `bcc', `cc', `fcc', and
`to'. Field and body (address) are separated by a colon
`:' and optionally blank (space, tabulator) characters.
The `shquote' expandaddr flag is supported. addr is
parsed like a message header address line, as if it would
be part of a template message fed in via -t, and the same
modifier suffix is supported. This option may be used
multiple times.

-t, --template
(Send mode) The text message given (on standard input) is
expected to contain, separated from the message body by an
empty line, one or multiple plain text message headers.
[v15 behaviour may differ] Readily prepared MIME mail
messages cannot be passed. Headers can span multiple
consecutive lines if follow lines start with any amount of
whitespace. A line starting with the number sign `#' in
the first column is ignored. Message recipients can be
given via the message headers `To:', `Cc:', `Bcc:' (the
`?single' modifier enforces treatment as a single
addressee, for example `To?single: exa, <m@ple>') or
`Fcc:', they will be added to any recipients specified on
the command line, and are likewise subject to expandaddr
validity checks. If a message subject is specified via
`Subject:' then it will be used in favour of one given on
the command line.

More optional headers are `Reply-To:' (possibly overriding
reply-to), `Sender:' (sender), `From:' (from and / or
option -r). `Message-ID:', `In-Reply-To:', `References:'
and `Mail-Followup-To:', by default created automatically
dependent on message context, will be used if specified (a
special address massage will however still occur for the
latter). Any other custom header field (also see -C,
customhdr and ~^) is passed through entirely unchanged,
and in conjunction with the options -~ or -# it is
possible to embed COMMAND ESCAPES. Also see -M, -m, -q.

-u user, --inbox-of=..
Initially read the primary system mailbox of user,
appropriate privileges presumed; effectively identical to
`-f %user'.

-V, --version
Show S-nails version and exit. The command version will
also show the list of features: `$ s-nail -:/ -Xversion
-Xx'.

-v, --verbose
sets the internal variable verbose to enable logging of
informational context messages. (Increases level of
verbosity when used multiple times.) Also see -d.

-X cmd, --startup-cmd=..
Add the given (or multiple for a multiline argument) cmd
to a list of commands to be executed before normal
operation starts. The commands will be evaluated as a
unit, just as via source. Correlates with -# and errexit.

-Y cmd, --cmd=..
Add the given (or multiple for a multiline argument) cmd
to a list of commands to be executed after normal
operation has started. The commands will be evaluated
successively in the given order, and as if given on the
program's standard input -- before interactive prompting
begins in interactive mode, after standard input has been
consumed otherwise.

-~, --enable-cmd-escapes
Enable COMMAND ESCAPES in (Compose mode) even in non-
interactive use cases. This can for example be used to
automatically format the composed message text before
sending the message:

$ ( echo 'line one. Word. Word2.';\
echo '~| /usr/bin/fmt -tuw66' ) |\
LC_ALL=C s-nail -d~:/ -Sttycharset=utf-8 bob@exam.ple

-#, --batch-mode
Enables batch mode: standard input is made line buffered,
the complete set of (interactive) commands is available,
processing of COMMAND ESCAPES is enabled in Compose mode,
and diverse INTERNAL VARIABLES are adjusted for batch
necessities, exactly as if done via -S: emptystart,
noerrexit, noheader, noposix, quiet, sendwait,
typescript-mode as well as MAIL, MBOX and inbox (the
latter three to /dev/null). Also, the values of COLUMNS
and LINES are looked up, and acted upon. The following
prepares an email message in a batched dry run:

$ for name in bob alice@exam.ple lisa@exam.ple; do
printf 'mail %s\n~s ubject\nText\n~.\n' "${name}"
done |
LC_ALL=C s-nail -#:x -Smta=test \
-X'alias bob bob@exam.ple'

-., --end-options
This flag forces termination of option processing in order
to prevent "option injection" (attacks). It also
forcefully puts S-nail into send mode, see On sending
mail, and non-interactive mode.

If the setting of expandargv allows their recognition all mta-option
arguments given at the end of the command line after a `--' separator
will be passed through to a file-based mta (Mail-Transfer-Agent) and
persist for the entire session. expandargv constraints do not apply to
the content of mta-arguments. Command line receiver address handling
supports the `shquote' constraint of expandaddr, for more please see On
sending mail, and non-interactive mode.

$ s-nail -#:/ -X 'addrcodec enc Hey, ho <silver@go>' -Xx

A starter

S-nail is a direct descendant of BSD Mail, itself a successor to the
Research UNIX mail which "was there from the start" according to
HISTORY. It thus represents the user side of the UNIX mail system,
whereas the system side (Mail-Transfer-Agent, MTA) was traditionally
taken by sendmail(8) (and most MTAs provide a binary of this name for
compatibility reasons). If the [Option]al SMTP mta is included in the
features of S-nail then the system side is not a mandatory precondition
for mail delivery.

S-nail strives for compliance with the POSIX mailx(1) standard, but
posix, one of the INTERNAL VARIABLES, or its ENVIRONMENTal equivalent
POSIXLY_CORRECT, needs to be set to adjust behaviour to be almost on
par. Almost, because there is one important difference: POSIX Shell-
style argument quoting is ([v15 behaviour may differ] increasingly)
used instead of the Old-style argument quoting that the standard
documents, which is believed to be a feature. The builtin as well as
the (default) global s-nail.rc Resource files already bend the standard
imposed settings a bit.

For example, hold and keepsave are set in order to suppress the
automatic moving of messages to the secondary mailbox MBOX that would
otherwise occur (see Message states), and keep to not remove empty
system MBOX mailbox files (or all empty such files in posix mode) to
avoid mangling of file permissions when files eventually get recreated.

To enter interactive mode even if the initial mailbox is empty
emptystart is set, editheaders to allow editing of headers as well as
fullnames to not strip down addresses in Compose mode, and quote to
include the message that is being responded to when replying, which is
indented by an indentprefix that also deviates from standard imposed
settings. mime-counter-evidence is fully enabled, too. It sets
followup-to-honour and reply-to-honour to comply with reply address
desires.

Credentials and other settings are easily addressable by grouping them
via account. The file mode creation mask can be managed with umask.
Files and shell pipe output can be sourced for evaluation, also during
startup from within the Resource files. Informational context can be
available by setting verbose or debug (as via -v, -d).

On sending mail, and non-interactive mode
To send a message to one or more people, using a local or built-in mta
(Mail-Transfer-Agent) transport to actually deliver the generated mail
message, S-nail can be invoked with arguments which are the names of
people to whom the mail will be sent, and the command line options -b
and -c can be used to add (blind) carbon copy receivers:

# Via test MTA
$ echo Hello, world | s-nail -:/ -Smta=test -s test $LOGNAME

# Via sendmail(1) MTA
$ </dev/null s-nail -:x -s test $LOGNAME

# Debug dry-run mode:
$ </dev/null LC_ALL=C s-nail -d -:/ \
-Sttycharset=utf8 -Sfullnames \
-b bcc@exam.ple -c cc@exam.ple -. \
'(Lovely) Bob <bob@exam.ple>' eric@exam.ple

# With SMTP (no real sending due to -d debug dry-run)
$ LC_ALL=C s-nail -d -:/ -Sv15-compat -Sttycharset=utf8 \
-S mta=smtps://mylogin@exam.ple:465 -Ssmtp-auth=none \
-S from=scriptreply@exam.ple \
-a /etc/mail.rc --end-options \
eric@exam.ple < /tmp/letter.txt

Email addresses and plain user names are subject to alternates
filtering, names only are first expanded through alias and mta-aliases.
An address in angle brackets consisting only of a valid local user
`<name>' will be converted to a fully qualified address if either
hostname is not set, or set to a non-empty value; if set to the empty
value the conversion is left up to the mta. By setting expandaddr
fine-grained control of recipient address types other than user names
and network addresses is possible. Recipients are classified as
follows: any name that starts with a vertical bar `|' character
specifies a command pipe - the command string following the `|' is
executed and the message is sent to its standard input; likewise, any
name that consists only of hyphen-minus `-' or starts with the
character solidus `/' or the character sequence dot solidus `./' is
treated as a file, regardless of the remaining content. Any other name
which contains a commercial at `@' character is a network address; Any
other name which starts with a plus sign `+' character is a mailbox
name; Any other name which contains a solidus `/' character but no
exclamation mark `!' or percent sign `%' character before is also a
mailbox name; What remains is treated as a network address. This
classification can be avoided by using a `Fcc:' header, see Compose
mode.

$ echo bla | s-nail -Sexpandaddr -s test ./mbox.mbox
$ echo bla | s-nail -Sexpandaddr -s test '|cat >> ./mbox.mbox'
$ echo safe | LC_ALL=C \
s-nail -:/ -Smta=test -Sv15-compat -Sttycharset=utf8 \
--set mime-force-sendout --set fullnames \
-S expandaddr=fail,-all,+addr,failinvaddr -s test \
--end-options 'Imagine John <cold@turk.ey>'

Before messages are sent they undergo editing in Compose mode. But
many settings are static and can be set more generally. The envelope
sender address for example is defined by from, explicitly defining an
originating hostname may be desirable, especially with the built-in
SMTP Mail-Transfer-Agent mta. Character sets for outgoing message and
MIME part content are configurable via sendcharsets, whereas input data
is assumed to be in ttycharset. Message data will be passed over the
wire in a mime-encoding, and MIME parts aka attachments need a
mimetype, usually taken out of The mime.types files. Saving copies of
sent messages in a record mailbox may be desirable - as for most
mailbox folder targets Filename transformations will be performed.

For the purpose of arranging a complete environment of settings that
can be switched to with a single command or command line option there
are accounts. Alternatively a flat configuration could be possible,
making use of so-called variable chains which automatically pick
`USER@HOST' or `HOST' context-dependent variants some variables
support: for example addressing `Folder pop3://yaa@exam.ple' would find
pop3-no-apop-yaa@exam.ple, pop3-no-apop-exam.ple and pop3-no-apop in
order. For more please see On URL syntax and credential lookup and
INTERNAL VARIABLES.

To avoid environmental noise scripts should create a script-local
environment, ideally with the command line options -: to disable
configuration files in conjunction with repetitions of -S to specify
variables:

$ env LC_ALL=C s-nail -:/ \
-Sv15-compat \
-Sttycharset=utf-8 -Smime-force-sendout \
-Sexpandaddr=fail,-all,failinvaddr \
-S mta=smtps://mylogin@exam.ple:465 -Ssmtp-auth=login \
-S from=scriptreply@exam.ple \
-s 'Subject to go' -a attachment_file \
-Sfullnames -. \
'Recipient 1 <rec1@exam.ple>' rec2@exam.ple \
< content_file

As shown, scripts producing messages can "fake" a locale environment,
the above specifies the all-compatible 7-bit clean LC_ALL "C", but will
nonetheless take and send UTF-8 in the message text by using
ttycharset. If character set conversion is compiled in (features
includes the term `,+iconv,') invalid (according to ttycharset)
character input data would normally cause errors; setting
mime-force-sendout will instead, as a last resort, classify the input
as binary data, and therefore allow message creation to be successful.
(Such content can then be inspected either by installing a
pipe-TYPE/SUBTYPE handler for `application/octet-stream', or possibly
automatically through mime-counter-evidence).

In interactive mode, introduced soon, messages can be sent by calling
the mail command with a list of recipient addresses:

$ s-nail -:/ -Squiet -Semptystart -Sfullnames -Smta=test
"/var/spool/mail/user": 0 messages
? mail "Recipient 1 <rec1@exam.ple>", rec2@exam.ple
...
? # Will do the right thing (tm)
? m rec1@exam.ple rec2@exam.ple

Compose mode

If standard input is a terminal rather than the message to be sent, the
user is expected to type in the message contents. In compose mode
lines beginning with the character `~' (in fact the value of escape)
are special - these are so-called COMMAND ESCAPES which can be used to
read in files, process shell commands, add and edit attachments and
more. For example ~v or ~e will start the VISUAL text EDITOR,
respectively, to revise the message in its current state, ~h allows
editing of the most important message headers, with the potent ~^
custom headers can be created, for example (more specifically than with
-C and customhdr). [Option]ally ~? gives an overview of most other
available command escapes.

To create file-carbon-copies the special recipient header `Fcc:' may be
used as often as desired, for example via ~^. Its entire value (or
body in standard terms) is interpreted as a folder target, after having
been subject to Filename transformations: this is the only way to
create a file-carbon-copy without introducing an ambiguity regarding
the interpretation of the address, file names with leading vertical
bars or commercial ats can be used. Like all other recipients `Fcc:'
is subject to the checks of expandaddr. Any local file and pipe
command addressee honours the setting of mbox-fcc-and-pcc.

Once finished with editing the command escape ~. (see there) will call
hooks, insert automatic injections and receivers, leave compose mode
and send the message once it is completed. Aborting letter composition
is possible with either of ~x or ~q, the latter of which will save the
message in the file denoted by DEAD unless nosave is set. And unless
ignoreeof is set the effect of ~. can also be achieved by typing end-
of-transmission (EOT) via `control-D' (`^D') at the beginning of an
empty line, and ~q is always reachable by typing end-of-text (ETX)
twice via `control-C' (`^C').

The compose mode hooks on-compose-enter, on-compose-splice,
on-compose-leave and on-compose-cleanup may be set to defined macros
and provide reliable and increasingly powerful mechanisms to perform
automated message adjustments dependent on message context, for example
addition of message signatures (message-inject-head,
message-inject-tail) or creation of additional receiver lists (also by
setting autocc, autobcc). To achieve that the command digmsg may be
used in order to query and adjust status of message(s). The splice
hook can also make use of COMMAND ESCAPES. ([v15 behaviour may differ]
The compose mode hooks work for forward, mail, reply and variants;
resend and Resend only provide the hooks on-resend-enter and
on-resend-cleanup, which are pretty restricted due to the nature of the
operation.)

On reading mail, and more on interactive mode
When invoked without addressees S-nail enters interactive mode in which
mails may be read. When used like that the user's system inbox (for
more on mailbox types please see the command folder) is read in and a
one line header of each message therein is displayed if the variable
header is set. The visual style of this summary of headers can be
adjusted through the variable headline and the possible sorting
criterion via autosort. Scrolling through screenfuls of headers can be
performed with the command z. If the initially opened mailbox is empty
S-nail will instead exit immediately (after displaying a message)
unless the variable emptystart is set.

At the prompt the command list will give a listing of all available
commands and help will [Option]ally give a summary of some common ones.
If the [Option]al documentation strings are available (see features)
one can type `help X' (or `?X') and see the actual expansion of `X' and
what its purpose is, i.e., commands can be abbreviated (note that POSIX
defines some abbreviations, so that the alphabetical order of commands
does not necessarily relate to the abbreviations; it is however
possible to define overwrites with commandalias). These commands can
also produce a more verbose output.

Messages are given numbers (starting at 1) which uniquely identify
messages; the current message - the "dot" - will either be the first
new message, or the first unread message, or the first message of the
mailbox; the internal variable showlast will instead cause usage of the
last message for this purpose. The command headers will display a
screenful of header summaries containing the "dot", whereas from will
display only the summaries of the given messages, defaulting to the
"dot".

Message content can be displayed with the command type (`t', alias
print). Here the variable crt controls whether and when S-nail will
use the configured PAGER for display instead of directly writing to the
user terminal screen, the sole difference to the command more, which
will always use the PAGER. The command top will instead only show the
first toplines of a message (maybe even compressed if topsqueeze is
set). Message display experience may improve by setting and adjusting
mime-counter-evidence, and also see HTML mail and MIME attachments.

By default the current message ("dot") is displayed, but like with many
other commands it is possible to give a fancy message specification
(see Specifying messages), for example `t:u' will display all unread
messages, `t.' will display the "dot", `t 1 5' will type the messages 1
and 5, `t 1-5' will type the messages 1 through 5, and `t-' and `t+'
will display the previous and the next message, respectively. The
command search (a more substantial alias for from) will display a
header summary of the given message specification list instead of their
content; the following will search for subjects:

? from '@Some subject to search for'

In the default setup all header fields of a message will be typed, but
fields can be white- or blacklisted for a variety of applications by
using the command headerpick, e.g., to restrict their display to a very
restricted set for type: `headerpick type retain from to cc subject'.
In order to display all header fields of a message regardless of
currently active ignore or retain lists, use the commands Type and Top;
Show will show the raw message content. Note that historically the
global s-nail.rc not only adjusts the list of displayed headers, but
also sets crt. ([v15 behaviour may differ] A yet somewhat restricted)
Reliable scriptable message inspection is available via digmsg.

Dependent upon the configuration a line editor (see the section On
terminal control and line editor) aims at making the user experience
with the many COMMANDS a bit nicer. When reading the system inbox, or
when -f (or folder) specified a mailbox explicitly prefixed with the
special `%:' modifier (to propagate it to a primary system mailbox),
then messages which have been read (see Message states) will be
automatically moved to a secondary mailbox, the user's MBOX file, when
the mailbox is left, either by changing the active mailbox or by
quitting S-nail - this automatic moving from a system- or primary- to
the secondary mailbox is not performed when the variable hold is set.
Messages can also be explicitly moved to other mailboxes, whereas copy
keeps the original message. write can be used to write out data
content of specific parts of messages.

After examining a message the user can reply `r' to the sender and all
recipients (which will also be placed in `To:' unless recipients-in-cc
is set), or Reply `R' exclusively to the sender(s). To comply with
with the receivers desired reply address the quadoptions
followup-to-honour and reply-to-honour should usually be set. The
commands Lreply and Lfollowup know how to apply a special addressee
massage, see Mailing lists. Dependent on the presence and value of
quote the message being replied to will be included in a quoted form.
forwarding a message will allow editing the new message: the original
message will be contained in the message body, adjusted according to
headerpick. It is possible to resend or Resend messages: the former
will add a series of `Resent-' headers, whereas the latter will not;
different to newly created messages editing is not possible and no copy
will be saved even with record unless the additional variable
record-resent is set. When sending, replying or forwarding messages
comments and full names will be stripped from recipient addresses
unless the internal variable fullnames is set.

Of course messages can be delete `d', and they can spring into
existence again via undelete, or when the S-nail session is ended via
the exit or xit commands to perform a quick program termation. To end
a mail processing session regularly and perform a full program exit one
may issue the command quit. It will, among others, move read messages
to the secondary mailbox MBOX as necessary, discard deleted messages in
the current mailbox, and update the [Option]al (see features) line
editor history-file. By the way, whenever the main event loop is about
to look out for the next input line it will trigger the hook
on-main-loop-tick.

HTML mail and MIME attachments

HTML-only messages become more and more common, and many messages come
bundled with a bouquet of MIME (Multipurpose Internet Mail Extensions)
parts and attachments. To get a notion of MIME types there is a built-
in default set, onto which the content of The mime.types files will be
added (as configured and allowed by mimetypes-load-control). Types can
also become registered and listed with the command mimetype. To
improve interaction with the faulty MIME part declarations of real life
mime-counter-evidence will allow verification of the given assertion,
and the possible provision of an alternative, better MIME type. Note
plain text parts will always be preferred in `multipart/alternative'
MIME messages unless mime-alternative-favour-rich is set.

Whereas a simple HTML-to-text filter for displaying HTML messages is
[Option]ally supported (indicated by `,+filter-html-tagsoup,' in
features), MIME types other than plain text cannot be handled directly.
To deal with specific non-text MIME types or file extensions programs
need to be registered which either prepare (re-)integrable plain text
versions of their input (a mode which is called copiousoutput), or
display the content externally, for example in a graphical window: the
latter type is only considered by and for the command mimeview.

To install a handler program for a MIME type an according
pipe-TYPE/SUBTYPE variable needs to be set; to define a handler for a
file extension pipe-EXTENSION can be used - these handlers take
precedence. [Option]ally mail user agent configuration is supported
(see The Mailcap files), and will be queried for display or quote
handlers after the former ones. Type-markers registered via mimetype
are the last possible source for information how to handle a MIME type.

For example, to display HTML messages integrated via the text browsers
lynx(1) or elinks(1), register a MathML MIME type and enable its plain
text display, and to open PDF attachments in an external PDF viewer,
asynchronously and with some other magic attached:

? if "$features" !% ,+filter-html-tagsoup,
? #set pipe-text/html='?* elinks -force-html -dump 1'
? set pipe-text/html='?* lynx -stdin -dump -force_html'
? # Display HTML as plain text instead
? #set pipe-text/html=?t
? endif

? mimetype ?t application/mathml+xml mathml

? wysh set pipe-application/pdf='?&=? \
trap "rm -f \"${MAILX_FILENAME_TEMPORARY}\"" EXIT;\
trap "trap \"\" INT QUIT TERM; exit 1" INT QUIT TERM;\
mupdf "${MAILX_FILENAME_TEMPORARY}"'

? define showhtml {
? \localopts yes
? \set mime-alternative-favour-rich pipe-text/html=?h?
? \type "$@"
? }
? \commandalias html \\call showhtml

Mailing lists

Known or subscribed-to mailing lists may be flagged in the summary of
headers (headline format character `%L'), and will gain special
treatment when sending mails: the variable followup-to-honour will
ensure that a `Mail-Followup-To:' header is honoured when a message is
being replied to (reply, followup, Lreply, Lfollowup), and followup-to
controls creation of this header when creating mails, if the necessary
user setup (from, sender); is available; then, it may also be created
automatically, for example when list-replying via Lreply or Lfollowup,
when followup or reply is used and the messages `Mail-Followup-To:' is
honoured etc.

The commands mlist and mlsubscribe manage S-nails notion of which
addresses are mailing lists. With the [Option]al regular expression
support any address which contains any of the magic regular expression
characters (`^[*+?|$'; see re_format(7) or regex(7), dependent on the
host system) will be compiled and used as one, possibly matching many
addresses. It is not possible to escape the "magic": in order to match
special characters as-is, bracket expressions must be used, for example
`search @subject@'[[]open bracket''.

? set followup-to followup-to-honour=ask-yes \
reply-to-honour=ask-yes
? mlist a1@b1.c1 a2@b2.c2 '.*@lists\.c3$'
? mlsubscribe a4@b4.c4 exact@lists.c3

Known and subscribed lists differ in that for the latter the users
address is not part of a generated `Mail-Followup-To:'. There are
exceptions, for example if multiple lists are addressed and not all
have the subscription attribute. When replying to a message its list
address (`List-Post:' header) is automatically and temporarily treated
like a known mlist; dependent on the variable reply-to-honour an
existing `Reply-To:' is used instead (if it is a single address on the
same domain as `List-Post:') in order to accept a list administrator's
wish that is supposed to have been manifested like that.

For convenience and compatibility with mail programs that do not honour
the non-standard M-F-T, an automatic user entry in the carbon-copy
`Cc:' address list of generated message can be created by setting
followup-to-add-cc. This entry will be added whenever the user will be
placed in the `Mail-Followup-To:' list, and is not a regular addressee
already. reply-to-swap-in tries to deal with the address rewriting
that many mailing-lists nowadays perform to work around DKIM / DMARC
etc. standard imposed problems.

Signed and encrypted messages with S/MIME
[Option] S/MIME provides two central mechanisms: message signing and
message encryption. A signed message contains some data in addition to
the regular text. The data can be used to verify that the message has
been sent using a valid certificate, that the sender address matches
that in the certificate, and that the message text has not been
altered. Signing a message does not change its regular text; it can be
read regardless of whether the recipients software is able to handle
S/MIME. It is thus usually possible to sign all outgoing messages if
so desired.

Encryption, in contrast, makes the message text invisible for all
people except those who have access to the secret decryption key. To
encrypt a message, the specific recipients public encryption key must
be known. It is therefore not possible to send encrypted mail to
people unless their key has been retrieved from either previous
communication or public key directories. Because signing is performed
with private keys, and encryption with public keys, messages should
always be signed before being encrypted.

A central concept to S/MIME is that of the certification authority
(CA). A CA is a trusted institution that issues certificates. For
each of these certificates it can be verified that it really originates
from the CA, provided that the CA's own certificate is previously
known. A set of CA certificates is usually delivered and installed
together with the cryptographical library that is used on the local
system. Therefore reasonable security for S/MIME on the Internet is
provided if the source that provides that library installation is
trusted. It is also possible to use a specific pool of trusted
certificates. If this is desired, smime-ca-no-defaults should be set
to avoid using the default certificate pool, and smime-ca-file and/or
smime-ca-dir should be pointed to a trusted pool of certificates. A
certificate cannot be more secure than the method its CA certificate
has been retrieved with.

This trusted pool of certificates is used by the command verify to
ensure that the given S/MIME messages can be trusted. If so, verified
sender certificates that were embedded in signed messages can be saved
locally with the command certsave, and used by S-nail to encrypt
further communication with these senders:

? certsave FILENAME
? set smime-encrypt-USER@HOST=FILENAME \
smime-cipher-USER@HOST=AES256

To sign outgoing messages, in order to allow receivers to verify the
origin of these messages, a personal S/MIME certificate is required.
S-nail supports password-protected personal certificates (and keys),
see smime-sign-cert. The section On URL syntax and credential lookup
gives an overview of the possible sources of user credentials, and
S/MIME step by step shows examplarily how a private S/MIME certificate
can be obtained. In general, if such a private key plus certificate
"pair" is available, all that needs to be done is to set some
variables:

? set smime-sign-cert=ME@exam.ple.paired \
smime-sign-digest=SHA512 \
smime-sign from=myname@my.host

Variables of interest for S/MIME in general are smime-ca-dir,
smime-ca-file, smime-ca-flags, smime-ca-no-defaults, smime-crl-dir,
smime-crl-file. For S/MIME signing of interest are smime-sign,
smime-sign-cert, smime-sign-include-certs and smime-sign-digest.
Additional variables of interest for S/MIME en- and decryption:
smime-cipher and smime-encrypt-USER@HOST. Variables of secondary
interest may be content-description-smime-message and
content-description-smime-signature. S/MIME is available if `,+smime,'
is included in features.

[v15 behaviour may differ] Note that neither S/MIME signing nor
encryption applies to message subjects or other header fields yet.
Thus they may not contain sensitive information for encrypted messages,
and cannot be trusted even if the message content has been verified.
When sending signed messages, it is recommended to repeat any important
header information in the message text.

On URL syntax and credential lookup

For accessing protocol-specific resources Uniform Resource Locators
(URL, RFC 3986) have become omnipresent. Here they are expected in a
"normalized" variant, not used in data exchange, but only meant as a
compact, easy-to-use way of defining and representing information in a
well-known notation; as such they do not conform to any real standard.
Optional parts are placed in brackets `[]', optional either because
there also exist other ways to define the information, or because the
part is protocol specific. `/path' for example is used by the
[Option]al Maildir folder type and the IMAP protocol, but not by POP3.
If `USER' and `PASSWORD' are included in an URL server specification,
URL percent encoded (RFC 3986) forms are needed, generable with
urlcodec.

PROTOCOL://[USER[:PASSWORD]@]server[:port][/path]

Often INTERNAL VARIABLES exist in multiple versions, called "variable
chains" in this document: the plain `variable' as well as
`variable-HOST' and `variable-USER@HOST'. If a port was specified
`HOST' really means `server:port', not `server'. And this `USER' is
never in URL percent encoded form. For example, whether the
hypothetical `smtp://wings%3Aof@a.dove' including user and password was
used, or whether it was `smtp://a.dove' and it came from a different
source, to lookup the chain tls-config-pairs first `tls-config-pairs-
wings:of@a.dove' is looked up, then `tls-config-pairs-a.dove', before
finally looking up the plain variable.

The logic to collect (an accounts) credential information is as
follows:

+o A user is always required. If no `USER' has been given in the URL
the variables user-HOST and user are looked up. Afterwards, when
enforced by the [Option]al variables netrc-lookup-HOST or
netrc-lookup, The .netrc file of the user will be searched for a
`HOST' specific entry which provides a `login' name: only
unambiguous entries are used (one possible matching entry for
`HOST').

If there is still no `USER' then the verified LOGNAME, known to be
a valid user on the current host, is used.

+o Authentication: unless otherwise noted the chain
PROTOCOL-auth-USER@HOST, PROTOCOL-auth-HOST, PROTOCOL-auth is
checked, falling back to a protocol-specific default as necessary.

+o If no `PASSWORD' has been given in the URL, then if the `USER' has
been found through the [Option]al netrc-lookup, that may have also
provided the password. Otherwise the chain password-USER@HOST,
password-HOST, password is looked up.

Thereafter the (now complete) [Option]al chain
netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup is checked,
if set the netrc cache is searched for a password only (multiple
user accounts for a single machine may exist as well as a fallback
entry without user but with a password).

If at that point there is still no password available, but the
(protocols') chosen authentication type requires a password, then
in interactive mode the user will be prompted on the terminal.

Note: S/MIME verification works relative to the values found in the
`From:' (or `Sender:') header field(s), which means the values of
smime-sign, smime-sign-cert, smime-sign-include-certs and
smime-sign-digest will not be looked up using the `USER' and `HOST'
chains from above, but instead use the corresponding values from the
message that is being worked on. If no address matches we assume and
use the setting of from. In unusual cases multiple and different
`USER' and `HOST' combinations may therefore be involved - on the other
hand those unusual cases become possible. The usual case is as short
as:

set mta=smtp://USER:PASS@HOST smtp-use-starttls \
smime-sign smime-sign-cert=+smime.pair \
from=myname@my.host

The section EXAMPLES contains complete example configurations.

Encrypted network communication

[Option] SSL (Secure Sockets Layer) aka its successor TLS (Transport
Layer Security) are protocols which aid in securing communication by
providing a safely initiated and encrypted network connection. A
central concept of TLS are certificates: as part of each network
connection setup a (set of) certificates will be exchanged through
which the identity of the network peer can be cryptographically
verified; if possible the TLS/SNI (ServerNameIndication) extension will
be enabled to allow servers fine-grained control over the certificates
being used. A locally installed pool of trusted certificates will then
be inspected, and verification will succeed if it contains a(n
in)direct signer of the presented certificate(s).

The local pool of trusted so-called CA (Certification Authority)
certificates is usually delivered with and used along the TLS library.
A custom pool of trusted certificates can be selected by pointing
tls-ca-file and/or (with special preparation) tls-ca-dir to the desired
location; setting tls-ca-no-defaults in addition will avoid additional
inspection of the default pool. A certificate cannot be more secure
than the method its CA certificate has been retrieved with. For
inspection or other purposes, the certificate of a server (as seen when
connecting to it) can be fetched with the command tls (port can usually
be the protocol name, too, and tls-verify is taken into account here):

$ s-nail -vX 'tls certchain SERVER-URL[:PORT]; x'

A local pool of CA certificates is not strictly necessary, however,
server certificates can also be verified via their fingerprint. For
this a message digest will be calculated and compared against the
variable chain tls-fingerprint, and verification will succeed if the
fingerprint matches. The message digest (algorithm) can be configured
via the variable chain tls-fingerprint-digest; tls can again be used:

$ s-nail -X 'wysh set verbose; tls fingerprint SERVER-URL[:PORT]; x'

It depends on the used protocol whether encrypted communication is
possible, and which configuration steps have to be taken to enable it.
Some protocols, like POP3S, are implicitly encrypted, others, like
POP3, can upgrade a plain text connection if so requested. For
example, to use the `STLS' that POP3 offers (a member of) the variable
(chain) pop3-use-starttls needs to be set, with convenience via
shortcut:

shortcut encpop1 pop3s://pop1.exam.ple

shortcut encpop2 pop3://pop2.exam.ple
set pop3-use-starttls-pop2.exam.ple

set mta=smtps://smtp.exam.ple:465
set mta=smtp://smtp.exam.ple smtp-use-starttls

Normally that is all there is to do, given that TLS libraries try to
provide safe defaults, plenty of knobs however exist to adjust
settings. For example certificate verification settings can be fine-
tuned via tls-ca-flags, and the TLS configuration basics are accessible
via tls-config-pairs, for example to control protocol versions or
cipher lists. In the past hints on how to restrict the set of
protocols to highly secure ones were indicated, but as of the time of
this writing the list of protocols or ciphers may need to become
relaxed in order to be able to connect to some servers; the following
example allows connecting to a "Lion" that uses OpenSSL 0.9.8za from
June 2014 (refer to INTERNAL VARIABLES for more on variable chains):

wysh set tls-config-pairs-lion@exam.ple='MinProtocol=TLSv1.1,\
CipherString=TLSv1.2:!aNULL:!eNULL:\
ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:\
DHE-RSA-AES256-SHA:@STRENGTH'

The OpenSSL program ciphers(1) should be referred to when creating a
custom cipher list. Variables of interest for TLS in general are
tls-ca-dir, tls-ca-file, tls-ca-flags, tls-ca-no-defaults,
tls-config-file, tls-config-module, tls-config-pairs, tls-crl-dir,
tls-crl-file, tls-rand-file as well as tls-verify. Also see
tls-features. TLS is available if `+tls' is included in features.

Character sets

[Option] The user's locale environment is detected by looking at the
LC_ALL environment variable. The internal variable ttycharset will be
set to the detected terminal character set accordingly, and will thus
show up in the output of commands like set and varshow. This character
set will be targeted when trying to display data, and user input data
is expected to be in this character set, too.

When creating messages their character input data is classified. 7-bit
clean text data and attachments will be classified as charset-7bit.
8-bit data will [Option]ally be converted into members of sendcharsets
until a character set conversion succeeds. charset-8bit is the implied
default last member of this list. If no 8-bit character set is capable
to represent input data, no message will be sent, and its text will
optionally be saved in DEAD. If that is not acceptable, for example in
script environments, mime-force-sendout can be set to force sending of
non-convertible data as `application/octet-stream' classified binary
content instead: like this receivers still have the option to inspect
message content (for example via mime-counter-evidence). If the
[Option]al character set conversion is not available (features misses
`,+iconv,'), ttycharset is the only supported character set for non
7-bit clean data, and it is simply assumed it can be used to exchange
8-bit messages.

ttycharset may also be given an explicit value to send mail in a
completely "faked" locale environment, which can be used to generate
and send for example 8-bit UTF-8 input data in a pure 7-bit US-ASCII
`LC_ALL=C' environment (an example of this can be found in the section
On sending mail, and non-interactive mode). Due to lack of programming
interfaces reading mail will not really work as expected in a faked
environment: whereas ttycharset might be addressable, any output will
be made safely printable, as via vexpr makeprint, according to the
actual locale environment, which is not affected by ttycharset.

Classifying 7-bit clean data as charset-7bit is a problem if the input
character set (ttycharset) is a multibyte character set that is itself
7-bit clean. For example, the Japanese character set ISO-2022-JP is,
but is capable to encode the rich set of Japanese Kanji, Hiragana and
Katakana characters: in order to notify receivers of this character set
the mail message must be MIME encoded so that the character set
ISO-2022-JP can be advertised, otherwise an invalid email message would
result! To achieve this, the variable charset-7bit can be set to
ISO-2022-JP. (Today a better approach regarding email is the usage of
UTF-8, which uses 8-bit bytes for non-US-ASCII data.)

When replying to a message and the variable reply-in-same-charset is
set, the character set of the message being replied to is tried first
as a target character set (still being a subject of charsetalias
filtering, however). Another opportunity is
sendcharsets-else-ttycharset to reflect the user's locale environment
automatically, it will treat ttycharset as an implied member of (an
unset) sendcharsets.

[Option] When reading messages, their text data is converted into
ttycharset as necessary in order to display them on the user's
terminal. Unprintable characters and invalid byte sequences are
detected and replaced by substitution characters. Character set
mappings for source character sets can be established with
charsetalias, which may be handy to work around faulty or incomplete
character set catalogues (one could for example add a missing LATIN1 to
ISO-8859-1 mapping), or to enforce treatment of one character set as
another one ("interpret LATIN1 as CP1252"). Also see
charset-unknown-8bit to deal with another hairy aspect of message
interpretation.

In general, if a message saying "cannot convert from a to b" appears,
either some characters are not appropriate for the currently selected
(terminal) character set, or the needed conversion is not supported by
the system. In the first case, it is necessary to set an appropriate
LC_CTYPE locale and/or the variable ttycharset. The best results are
usually achieved when running in a UTF-8 locale on a UTF-8 capable
terminal, in which case the full Unicode spectrum of characters is
available. In this setup characters from various countries can be
displayed, while it is still possible to use more simple character sets
for sending to retain maximum compatibility with older mail clients.

On the other hand the POSIX standard defines a locale-independent 7-bit
"portable character set" that should be used when overall portability
is an issue, the even more restricted subset named "portable filename
character set" consists of A-Z, a-z, 0-9, period `.', underscore `_'
and hyphen-minus `-'.

Message states

S-nail differentiates in between several message states; the current
state will be reflected in the summary of headers if the attrlist of
the configured headline allows, and Specifying messages dependent on
their state is possible. When operating on the system inbox, or in any
other primary system mailbox, special actions, like the automatic
moving of messages to the secondary mailbox MBOX, may be applied when
the mailbox is left (also implicitly by program termination, unless the
command exit was used) - however, because this may be irritating to
users which are used to "more modern" mail-user-agents, the provided
global s-nail.rc template sets the internal hold and keepsave variables
in order to suppress this behaviour.

`new' Message has neither been viewed nor moved to any other
state. Such messages are retained even in the primary
system mailbox.

`unread' Message has neither been viewed nor moved to any other
state, but the message was present already when the mailbox
has been opened last: Such messages are retained even in
the primary system mailbox.

`read' The message has been processed by one of the following
commands: ~f, ~m, ~F, ~M, copy, mbox, next, pipe, Print,
print, top, Type, type, undelete. The commands dp and dt
will always try to automatically "step" and type the "next"
logical message, and may thus mark multiple messages as
read, the delete command will do so if the internal
variable autoprint is set.

Except when the exit command is used, messages that are in
a primary system mailbox and are in `read' state when the
mailbox is left will be saved in the secondary mailbox MBOX
unless the internal variable hold it set.

`deleted' The message has been processed by one of the following
commands: delete, dp, dt. Only undelete can be used to
access such messages.

`preserved' The message has been processed by a preserve command and it
will be retained in its current location.

`saved' The message has been processed by one of the following
commands: save or write. Unless when the exit command is
used, messages that are in a primary system mailbox and are
in `saved' state when the mailbox is left will be deleted;
they will be saved in the secondary mailbox MBOX when the
internal variable keepsave is set.

In addition to these message states, flags which otherwise have no
technical meaning in the mail system except allowing special ways of
addressing them when Specifying messages can be set on messages. These
flags are saved with messages and are thus persistent, and are portable
between a set of widely used MUAs.

answered Mark messages as having been answered.

draft Mark messages as being a draft.

flag Mark messages which need special attention.

Specifying messages

[Only new quoting rules] COMMANDS which take Message list arguments,
such as search, type, copy, and delete, can perform actions on a number
of messages at once. Specifying invalid messages, or using illegal
syntax, will cause errors to be reported through the INTERNAL VARIABLES
!, ^ERR and companions, as well as the command exit status ?.

For example, `delete 1 2' deletes the messages 1 and 2, whereas `delete
1-5' will delete the messages 1 through 5. In sorted or threaded mode
(see the sort command), `delete 1-5' will delete the messages that are
located between (and including) messages 1 through 5 in the
sorted/threaded order, as shown in the headers summary.

Errors can for example be ^ERR-BADMSG when requesting an invalid
message, ^ERR-NOMSG if no applicable message can be found,
^ERR-CANCELED for missing informational data (mostly thread-related).
^ERR-INVAL for invalid syntax as well as ^ERR-IO for input/output
errors can happen. The following special message names exist:

. The current message, the so-called "dot".

; The message that was previously the current message; needs
to be quoted.

, The parent message of the current message, that is the
message with the Message-ID given in the `In-Reply-To:'
field or the last entry of the `References:' field of the
current message.

- The previous undeleted message, or the previous deleted
message for the undelete command; In sorted or `thread'ed
mode, the previous such message in the according order.

+ The next undeleted message, or the next deleted message
for the undelete command; In sorted or `thread'ed mode,
the next such message in the according order.

^ The first undeleted message, or the first deleted message
for the undelete command; In sorted or `thread'ed mode,
the first such message in the according order.

$ The last message; In sorted or `thread'ed mode, the last
such message in the according order. Needs to be quoted.

&x In `thread'ed sort mode, selects the message addressed
with x, where x is any other message specification, and
all messages from the thread that begins at it. Otherwise
it is identical to x. If x is omitted, the thread
beginning with the current message is selected.

* All messages.

` All messages that were included in the Message list
arguments of the previous command; needs to be quoted. (A
convenient way to read all new messages is to select them
via `from :n', as below, and then to read them in order
with the default command -- next -- simply by successively
typing ``'; for this to work showlast must be set.)

x-y An inclusive range of message numbers. Selectors that may
also be used as endpoints include any of .;-+^$.

address A case-insensitive "any substring matches" search against
the `From:' header, which will match addresses (too) even
if showname is set (and POSIX says "any address as shown
in a header summary shall be matchable in this form");
However, if the allnet variable is set, only the local
part of the address is evaluated for the comparison, not
ignoring case, and the setting of showname is completely
ignored. For finer control and match boundaries use the
`@' search expression.

/string All messages that contain string in the subject field
(case ignored according to locale). See also the
searchheaders variable. If string is empty, the string
from the previous specification of that type is used
again.

[@name-list]@expr
All messages that contain the given case-insensitive
search expression; If the [Option]al regular expression
support is available expr will be interpreted as (an
extended) one if any of the magic regular expression
characters is seen. If the optional @name-list part is
missing the search is restricted to the subject field
body, but otherwise name-list specifies a comma-separated
list of header fields to search, for example

'@to,from,cc@Someone i ought to know'

In order to search for a string that includes a `@'
(commercial at) character the name-list is effectively
non-optional, but may be given as the empty string. Also,
specifying an empty search expression will effectively
test for existence of the given header fields. Some
special header fields may be abbreviated: `f', `t', `c',
`b' and `s' will match `From', `To', `Cc', `Bcc' and
`Subject', respectively and case-insensitively.
[Option]ally, and just like expr, name-list will be
interpreted as (an extended) regular expression if any of
the magic regular expression characters is seen.

The special names `header' or `<' can be used to search in
(all of) the header(s) of the message, and the special
names `body' or `>' and `text' or `=' will perform full
text searches - whereas the former searches only the body,
the latter also searches the message header ([v15
behaviour may differ] this mode yet brute force searches
over the entire decoded content of messages, including
administrativa strings).

This specification performs full text comparison, but even
with regular expression support it is almost impossible to
write a search expression that safely matches only a
specific address domain. To request that the body content
of the header is treated as a list of addresses, and to
strip those down to the plain email address which the
search expression is to be matched against, prefix the
effective name-list with a tilde `~':

'@~f,c@@a\.safe\.domain\.match$'

:c All messages of state or with matching condition `c',
where `c' is one or multiple of the following colon
modifiers:

a answered messages (cf. the variable
markanswered).
d `deleted' messages (for the undelete and from
commands only).
f flagged messages.
L Messages with receivers that match mlsubscribed
addresses.
l Messages with receivers that match mlisted
addresses.
n `new' messages.
o Old messages (any not in state `read' or
`new').
r `read' messages.
S [Option] Messages with unsure spam
classification (see Handling spam).
s [Option] Messages classified as spam.
t Messages marked as draft.
u `unread' messages.

[Option] IMAP-style SEARCH expressions may also be used. These consist
of keywords and criterions, and because Message list arguments are
split into tokens according to Shell-style argument quoting it is
necessary to quote the entire IMAP search expression in order to ensure
that it remains a single token. This addressing mode is available with
all types of mailbox folders; S-nail will perform the search locally as
necessary. Strings must be enclosed by double quotation marks `"' in
their entirety if they contain whitespace or parentheses; within the
quotes, only reverse solidus `\' is recognized as an escape character.
All string searches are case-insensitive. When the description
indicates that the "envelope" representation of an address field is
used, this means that the search string is checked against both a list
constructed as

'("name" "source" "local-part" "domain-part")'

for each address, and the addresses without real names from the
respective header field. These search expressions can be nested using
parentheses, see below for examples.

(criterion) All messages that satisfy the given criterion.
(criterion1 criterion2 ... criterionN)
All messages that satisfy all of the given criteria.
(or criterion1 criterion2)
All messages that satisfy either criterion1 or criterion2,
or both. To connect more than two criteria using `or'
specifications have to be nested using additional
parentheses, as with `(or a (or b c))', since `(or a b c)'
really means `((a or b) and c)'. For a simple `or'
operation of independent criteria on the lowest nesting
level, it is possible to achieve similar effects by using
three separate criteria, as with `(a) (b) (c)'.
(not criterion)
All messages that do not satisfy criterion.
(bcc "string")
All messages that contain string in the envelope
representation of the `Bcc:' field.
(cc "string")
All messages that contain string in the envelope
representation of the `Cc:' field.
(from "string")
All messages that contain string in the envelope
representation of the `From:' field.
(subject "string")
All messages that contain string in the `Subject:' field.
(to "string")
All messages that contain string in the envelope
representation of the `To:' field.
(header name "string")
All messages that contain string in the specified `Name:'
field.
(body "string")
All messages that contain string in their body.
(text "string")
All messages that contain string in their header or body.
(larger size)
All messages that are larger than size (in bytes).
(smaller size)
All messages that are smaller than size (in bytes).
(before date)
All messages that were received before date, which must be
in the form `d[d]-mon-yyyy', where `d' denotes the day of
the month as one or two digits, `mon' is the name of the
month - one of `Jan Feb Mar Apr May Jun Jul Aug Sep Oct
Nov Dec', and `yyyy' is the year as four digits, for
example `28-Dec-2012'.
(on date) All messages that were received on the specified date.
(since date)
All messages that were received since the specified date.
(sentbefore date)
All messages that were sent on the specified date.
(senton date)
All messages that were sent on the specified date.
(sentsince date)
All messages that were sent since the specified date.
() The same criterion as for the previous search. This
specification cannot be used as part of another criterion.
If the previous command line contained more than one
independent criterion then the last of those criteria is
used.

On terminal control and line editor

[Option] Terminal control through one of the standard UNIX libraries,
library "libtermcap" or library "libterminfo", may be available. For
the TERMinal defined in the environment interactive usage aspects, for
example Coloured display, and insight of cursor and function keys for
the Mailx-Line-Editor (MLE), will be enhanced or enabled. Library
interaction can be disabled on a per-invocation basis via
termcap-disable, whereas the internal variable termcap is always used
as a preferred source of terminal capabilities. (For a usage example
see the FAQ entry Not "defunctional", but the editor key does not
work.)

[Option] The built-in Mailx-Line-Editor (MLE) should work in all
environments which comply to the ISO C standard ISO/IEC 9899/AMD1:1995
("ISO C90, Amendment 1"), and will support wide glyphs if possible (the
necessary functionality had been removed from ISO C, but was included
in X/Open Portability Guide Issue 4 ("XPG4")). Usage of a line editor
in interactive mode can be prevented by setting line-editor-disable.
Especially if the [Option]al terminal control support is missing
setting entries in termcap will help shall the MLE misbehave, see there
for more. The MLE can support a little bit of colour.

[Option] If the history feature is available then input from line
editor prompts will be saved in a history list that can be searched in
and be expanded from. Such saving can be prevented by prefixing input
with any amount of whitespace. Aspects of history, like allowed
content and maximum size, as well as whether history shall be saved
persistently, can be configured with the internal variables
history-file, history-gabby, history-gabby-persist and history-size.
There also exists the macro hook on-history-addition which can be used
to apply finer control on what enters history.

The MLE supports a set of editing and control commands. By default
(as) many (as possible) of these will be assigned to a set of single-
letter control codes, which should work on any terminal (and can be
generated by holding the "control" key while pressing the key of
desire, for example `control-D'). If the [Option]al bind command is
available then the MLE commands can also be accessed freely by
assigning the command name, which is shown in parenthesis in the list
below, to any desired key-sequence, and the MLE will instead and also
use bind to establish its built-in key bindings (more of them if the
[Option]al terminal control is available), an action which can then be
suppressed completely by setting line-editor-no-defaults. Shell-style
argument quoting notation is used in the following:

`\cA' Go to the start of the line (mle-go-home).
`\cB' Move the cursor backward one character (mle-go-bwd).
`\cC' raise(3) `SIGINT' (mle-raise-int).
`\cD' Forward delete the character under the cursor; quits S-nail
if used on the empty line unless the internal variable
ignoreeof is set (mle-del-fwd).
`\cE' Go to the end of the line (mle-go-end).
`\cF' Move the cursor forward one character (mle-go-fwd).
`\cG' Cancel current operation, full reset. If there is an
active history search or tabulator expansion then this
command will first reset that, reverting to the former line
content; thus a second reset is needed for a full reset in
this case (mle-reset).
`\cH' Backspace: backward delete one character (mle-del-bwd).
`\cI' [Only new quoting rules] Horizontal tabulator: try to
expand the word before the cursor, supporting the usual
Filename transformations (mle-complete; this is affected by
mle-quote-rndtrip and line-editor-cpl-word-breaks).
`\cJ' Newline: commit the current line (mle-commit).
`\cK' Cut all characters from the cursor to the end of the line
(mle-snarf-end).
`\cL' Repaint the line (mle-repaint).
`\cN' [Option] Go to the next history entry (mle-hist-fwd).
`\cO' ([Option]ally context-dependent) Invokes the command dt.
`\cP' [Option] Go to the previous history entry (mle-hist-bwd).
`\cQ' Toggle roundtrip mode shell quotes, where produced, on and
off (mle-quote-rndtrip). This setting is temporary, and
will be forgotten once the command line is committed; also
see shcodec.
`\cR' [Option] Complete the current line from (the remaining)
older history entries (mle-hist-srch-bwd).
`\cS' [Option] Complete the current line from (the remaining)
newer history entries (mle-hist-srch-fwd).
`\cT' Paste the snarf buffer (mle-paste).
`\cU' The same as `\cA' followed by `\cK' (mle-snarf-line).
`\cV' Prompts for a Unicode character (hexadecimal number without
prefix, see vexpr) to be inserted (mle-prompt-char). Note
this command needs to be assigned to a single-letter
control code in order to become recognized and executed
during input of a key-sequence (only three single-letter
control codes can be used for that shortcut purpose); this
control code is then special-treated and thus cannot be
part of any other sequence (because it will trigger the
mle-prompt-char function immediately).
`\cW' Cut the characters from the one preceding the cursor to the
preceding word boundary (mle-snarf-word-bwd).
`\cX' Move the cursor forward one word boundary
(mle-go-word-fwd).
`\cY' Move the cursor backward one word boundary
(mle-go-word-bwd).
`\cZ' raise(3) `SIGTSTP' (mle-raise-tstp).
`\c[' Escape: reset a possibly used multibyte character input
state machine and [Option]ally a lingering, incomplete key
binding (mle-cancel). This command needs to be assigned to
a single-letter control code in order to become recognized
and executed during input of a key-sequence (only three
single-letter control codes can be used for that shortcut
purpose). This control code may also be part of a multi-
byte sequence, but if a sequence is active and the very
control code is currently also an expected input, then the
active sequence takes precedence and will consume the
control code.
`\c\' ([Option]ally context-dependent) Invokes the command `z+'.
`\c]' ([Option]ally context-dependent) Invokes the command `z$'.
`\c^' ([Option]ally context-dependent) Invokes the command `z0'.
`\c_' Cut the characters from the one after the cursor to the
succeeding word boundary (mle-snarf-word-fwd).
`\c?' Backspace: mle-del-bwd.
- mle-bell: ring the audible bell.
- [Option] mle-clear-screen: move the cursor home and clear
the screen.
- mle-fullreset: different to mle-reset this will immediately
reset a possibly active search etc.
- mle-go-screen-bwd: move the cursor backward one screen
width.
- mle-go-screen-fwd: move the cursor forward one screen
width.
- mle-raise-quit: raise(3) `SIGQUIT'.

Coloured display

[Option] Colours and font attributes through ANSI a.k.a. ISO 6429 SGR
(select graphic rendition) escape sequences are optionally supported.
Usage of colours and font attributes solely depends upon the capability
of the detected terminal type (TERM), and as fine-tuned through
termcap. Colours and font attributes can be managed with the
multiplexer command colour, and uncolour removes the given mappings.
Setting colour-disable suppresses usage of colour and font attribute
sequences, while leaving established mappings unchanged.

Whether actually applicable colour and font attribute sequences should
also be generated when output is going to be paged through the external
PAGER (also see crt) depends upon the setting of colour-pager, because
pagers usually need to be configured in order to support ISO escape
sequences. Knowledge of some widely used pagers is however built-in,
and in a clean environment it is often enough to simply set
colour-pager; please refer to that variable for more on this topic.

It might make sense to conditionalize colour setup on interactive mode
via if (`terminal' indeed means "interactive"):

if terminal && "$features" =% ,+colour,
colour iso view-msginfo ft=bold,fg=green
colour iso view-header ft=bold,fg=red (from|subject) # regex
colour iso view-header fg=red

uncolour iso view-header from,subject
colour iso view-header ft=bold,fg=magenta,bg=cyan
colour 256 view-header ft=bold,fg=208,bg=230 "subject,from"
colour mono view-header ft=bold
colour mono view-header ft=bold,ft=reverse subject,from
endif

Handling spam

[Option] S-nail can make use of several spam interfaces for the purpose
of identification of, and, in general, dealing with spam messages. A
precondition of most commands in order to function is that the
spam-interface variable is set to one of the supported interfaces.
Specifying messages that have been identified as spam is possible via
their (volatile) `is-spam' state by using the `:s' and `:S'
specifications, and their attrlist entries will be used when displaying
the headline in the summary of headers.

+o spamrate rates the given messages and sets their `is-spam' flag
accordingly. If the spam interface offers spam scores these can be
shown in headline by using the format `%$'.

+o spamham, spamspam and spamforget will interact with the Bayesian
filter of the chosen interface and learn the given messages as
"ham" or "spam", respectively; the last command can be used to
cause "unlearning" of messages; it adheres to their current
`is-spam' state and thus reverts previous teachings.

+o spamclear and spamset will simply set and clear, respectively, the
mentioned volatile `is-spam' message flag, without any interface
interaction.

The spamassassin(1) based spam-interface `spamc' requires a running
instance of the spamd(1) server in order to function, started with the
option --allow-tell shall Bayesian filter learning be possible.

$ spamd -i localhost:2142 -i /tmp/.spamsock -d [-L] [-l]
$ spamd --listen=localhost:2142 --listen=/tmp/.spamsock \
--daemonize [--local] [--allow-tell]

Thereafter S-nail can make use of these interfaces:

$ s-nail -Sspam-interface=spamc -Sspam-maxsize=500000 \
-Sspamc-command=/usr/local/bin/spamc \
-Sspamc-arguments="-U /tmp/.spamsock" -Sspamc-user=
or
$ s-nail -Sspam-interface=spamc -Sspam-maxsize=500000 \
-Sspamc-command=/usr/local/bin/spamc \
-Sspamc-arguments="-d localhost -p 2142" -Sspamc-user=

Using the generic filter approach allows usage of programs like
bogofilter(1). Here is an example, requiring it to be accessible via
PATH:

$ s-nail -Sspam-interface=filter -Sspam-maxsize=500000 \
-Sspamfilter-ham="bogofilter -n" \
-Sspamfilter-noham="bogofilter -N" \
-Sspamfilter-nospam="bogofilter -S" \
-Sspamfilter-rate="bogofilter -TTu 2>/dev/null" \
-Sspamfilter-spam="bogofilter -s" \
-Sspamfilter-rate-scanscore="1;^(.+)$"

Because messages must exist on local storage in order to be scored (or
used for Bayesian filter training), it is possibly a good idea to
perform the local spam check last. Spam can be checked automatically
when opening specific folders by setting a specialized form of the
internal variable folder-hook.

define spamdelhook {
# Server side DCC
spamset (header x-dcc-brand-metrics "bulk")
# Server-side spamassassin(1)
spamset (header x-spam-flag "YES")
del :s # TODO we HAVE to be able to do `spamrate :u ! :sS'
move :S +maybe-spam
spamrate :u
del :s
move :S +maybe-spam
}
set folder-hook-SOMEFOLDER=spamdelhook

See also the documentation for the variables spam-interface,
spam-maxsize, spamc-command, spamc-arguments, spamc-user,
spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate
and spamfilter-rate-scanscore.

COMMANDS

S-nail reads input in lines. An unquoted reverse solidus `\' at the
end of a command line "escapes" the newline character: it is discarded
and the next line of input is used as a follow-up line, with all
leading whitespace removed; once an entire line is completed, the
whitespace characters space, tabulator, newline as well as those
defined by the variable ifs are removed from the beginning and end.
Placing any whitespace characters at the beginning of a line will
prevent a possible addition of the command line to the [Option]al
history.

The beginning of such input lines is then scanned for the name of a
known command: command names may be abbreviated, in which case the
first command that matches the given prefix will be used. Command
modifiers may prefix a command in order to modify its behaviour. A
name may also be a commandalias, which will become expanded until no
more expansion is possible. Once the command that shall be executed is
known, the remains of the input line will be interpreted according to
command-specific rules, documented in the following.

This behaviour is different to the sh(1)ell, which is a programming
language with syntactic elements of clearly defined semantics, and
therefore capable to sequentially expand and evaluate individual
elements of a line. `? set one=value two=$one' for example will never
possibly assign value to one, because the variable assignment is
performed no sooner but by the command (set), long after the expansion
happened.

A list of all commands in lookup order is dumped by the command list.
[Option]ally the command help (or ?), when given an argument, will show
a documentation string for the command matching the expanded argument,
as in `?t', which should be a shorthand of `?type'; with these
documentation strings both commands support a more verbose listing mode
which includes the argument type of the command and other information
which applies; a handy suggestion might thus be:

? define __xv {
# Before v15: need to enable sh(1)ell-style on _entire_ line!
localopts yes;wysh set verbose;ignerr eval "${@}";return ${?}
}
? commandalias xv '\call __xv'
? xv help set

Command modifiers

Commands may be prefixed by none to multiple command modifiers. Some
command modifiers can be used with a restricted set of commands only,
the verbose version of list will ([Option]ally) show which modifiers
apply.

+o The modifier reverse solidus \, to be placed first, prevents
commandalias expansions on the remains of the line, for example
`\echo' will always evaluate the command echo, even if an
(command)alias of the same name exists. commandalias content may
itself contain further command modifiers, including an initial
reverse solidus to prevent further expansions.

+o The modifier ignerr indicates that any error generated by the
following command should be ignored by the state machine and not
cause a program exit with enabled errexit or for the standardized
exit cases in posix mode. ?, one of the INTERNAL VARIABLES, will
be set to the real exit status of the command regardless.

+o local will alter the called command to apply changes only
temporarily, local to block-scope, and can thus only be used inside
of a defined macro or an account definition. Specifying it implies
the modifier wysh. Local variables will not be inherited by macros
deeper in the call chain, and all local settings will be garbage
collected once the local scope is left. To record and unroll
changes in the global scope use the command localopts.

+o scope does yet not implement any functionality.

+o u does yet not implement any functionality.

+o Some commands support the vput modifier: if used, they expect the
name of a variable, which can itself be a variable, i.e., shell
expansion is applied, as their first argument, and will place their
computation result in it instead of the default location (it is
usually written to standard output).

The given name will be tested for being a valid sh(1) variable
name, and may therefore only consist of upper- and lowercase
characters, digits, and the underscore; the hyphen-minus may be
used as a non-portable extension; digits may not be used as first,
hyphen-minus may not be used as last characters. In addition the
name may either not be one of the known INTERNAL VARIABLES, or must
otherwise refer to a writable (non-boolean) value variable. The
actual put operation may fail nonetheless, for example if the
variable expects a number argument only a number will be accepted.
Any error during these operations causes the command as such to
fail, and the error number ! will be set to ^ERR-NOTSUP, the exit
status ? should be set to `-1', but some commands deviate from the
latter, which is documented.

+o Last, but not least, the modifier wysh can be used for some old and
established commands to choose the new Shell-style argument quoting
rules over the traditional Old-style argument quoting. This
modifier is implied if v15-compat is set to a non-empty value.

Old-style argument quoting
[v15 behaviour may differ] This section documents the traditional and
POSIX standardized style of quoting non-message list arguments to
commands which expect this type of arguments: whereas still used by the
majority of such commands, the new Shell-style argument quoting may be
available even for those via wysh, one of the Command modifiers.
Nonetheless care must be taken, because only new commands have been
designed with all the capabilities of the new quoting rules in mind,
which can, for example generate control characters.

+o An argument can be enclosed between paired double-quotes
`"argument"' or single-quotes `'argument''; any whitespace,
shell word expansion, or reverse solidus characters (except
as described next) within the quotes are treated literally as
part of the argument. A double-quote will be treated
literally within single-quotes and vice versa. Inside such a
quoted string the actually used quote character can be used
nonetheless by escaping it with a reverse solidus `\', as in
`"y\"ou"'.

+o An argument that is not enclosed in quotes, as above, can
usually still contain space characters if those spaces are
reverse solidus escaped, as in `you\ are'.

+o A reverse solidus outside of the enclosing quotes is
discarded and the following character is treated literally as
part of the argument.

Shell-style argument quoting
sh(1)ell-style, and therefore POSIX standardized, argument parsing and
quoting rules are used by most commands. [v15 behaviour may differ]
Most new commands only support these new rules and are flagged [Only
new quoting rules], some elder ones can use them with the command
modifier wysh; in the future only this type of argument quoting will
remain.

A command line is parsed from left to right and an input token is
completed whenever an unquoted, otherwise ignored, metacharacter is
seen. Metacharacters are vertical bar |, ampersand &, semicolon ;, as
well as all characters from the variable ifs, and / or space,
tabulator, newline. The additional metacharacters left and right
parenthesis (, ) and less-than and greater-than signs <, > that the
sh(1) supports are not used, and are treated as ordinary characters:
for one these characters are a vivid part of email addresses, and it
seems highly unlikely that their function will become meaningful to S-
nail.

Compatibility note: [v15 behaviour may differ] Please note that
even many new-style commands do not yet honour ifs to parse their
arguments: whereas the sh(1)ell is a language with syntactic
elements of clearly defined semantics, S-nail parses entire input
lines and decides on a per-command base what to do with the rest
of the line. This also means that whenever an unknown command is
seen all that S-nail can do is cancellation of the processing of
the remains of the line.

It also often depends on an actual subcommand of a multiplexer
command how the rest of the line should be treated, and until v15
we are not capable to perform this deep inspection of arguments.
Nonetheless, at least the following commands which work with
positional parameters fully support ifs for an almost shell-
compatible field splitting: call, call_if, read, vpospar, xcall.

Any unquoted number sign `#' at the beginning of a new token starts a
comment that extends to the end of the line, and therefore ends
argument processing. An unquoted dollar sign `$' will cause variable
expansion of the given name, which must be a valid sh(1)ell-style
variable name (see vput): INTERNAL VARIABLES as well as ENVIRONMENT
(shell) variables can be accessed through this mechanism, brace
enclosing the name is supported (i.e., to subdivide a token).

Whereas the metacharacters space, tabulator, newline only complete an
input token, vertical bar |, ampersand & and semicolon ; also act as
control operators and perform control functions. For now supported is
semicolon ;, which terminates a single command, therefore sequencing
the command line and making the remainder of the line a subject to
reevaluation. With sequencing, multiple command argument types and
quoting rules may therefore apply to a single line, which can become
problematic before v15: e.g., the first of the following will cause
surprising results.

? echo one; set verbose; echo verbose=$verbose.
? echo one; wysh set verbose; echo verbose=$verbose.

Quoting is a mechanism that will remove the special meaning of
metacharacters and reserved words, and will prevent expansion. There
are four quoting mechanisms: the escape character, single-quotes,
double-quotes and dollar-single-quotes:

+o The literal value of any character can be preserved by
preceding it with the escape character reverse solidus `\'.

+o Arguments which are enclosed in `'single-quotes'' retain
their literal value. A single-quote cannot occur within
single-quotes.

+o The literal value of all characters enclosed in `"double-
quotes"' is retained, with the exception of dollar sign `$',
which will cause variable expansion, as above, backquote
(grave accent) ``', (which not yet means anything special),
reverse solidus `\', which will escape any of the characters
dollar sign `$' (to prevent variable expansion), backquote
(grave accent) ``', double-quote `"' (to prevent ending the
quote) and reverse solidus `\' (to prevent escaping, i.e., to
embed a reverse solidus character as-is), but has no special
meaning otherwise.

+o Arguments enclosed in `$'dollar-single-quotes'' extend normal
single quotes in that reverse solidus escape sequences are
expanded as follows:

`\a' bell control character (ASCII and ISO-10646 BEL).
`\b' backspace control character (ASCII and ISO-10646
BS).
`\E' escape control character (ASCII and ISO-10646 ESC).
`\e' the same.
`\f' form feed control character (ASCII and ISO-10646
FF).
`\n' line feed control character (ASCII and ISO-10646
LF).
`\r' carriage return control character (ASCII and
ISO-10646 CR).
`\t' horizontal tabulator control character (ASCII and
ISO-10646 HT).
`\v' vertical tabulator control character (ASCII and
ISO-10646 VT).
`\\' emits a reverse solidus character.
`\'' single quote.
`\"' double quote (escaping is optional).
`\NNN' eight-bit byte with the octal value `NNN' (one to
three octal digits), optionally prefixed by an
additional `0'. A 0 byte will suppress further
output for the quoted argument.
`\xHH' eight-bit byte with the hexadecimal value `HH' (one
or two hexadecimal characters, no prefix, see
vexpr). A 0 byte will suppress further output for
the quoted argument.
`\UHHHHHHHH'
the Unicode / ISO-10646 character with the
hexadecimal codepoint value `HHHHHHHH' (one to
eight hexadecimal characters) -- note that Unicode
defines the maximum codepoint ever to be supported
as `0x10FFFF' (in planes of `0xFFFF' characters
each). This escape is only supported in locales
that support Unicode (see Character sets), in other
cases the sequence will remain unexpanded unless
the given code point is ASCII compatible or (if the
[Option]al character set conversion is available)
can be represented in the current locale. The
character NUL will suppress further output for the
quoted argument.
`\uHHHH' Identical to `\UHHHHHHHH' except it takes only one
to four hexadecimal characters.
`\cX' Emits the non-printable (ASCII and compatible) C0
control codes 0 (NUL) to 31 (US), and 127 (DEL).
Printable representations of ASCII control codes
can be created by mapping them to a different,
visible part of the ASCII character set. Adding
the number 64 achieves this for the codes 0 to 31,
here 7 (BEL): `7 + 64 = 71 = G'. The real
operation is a bitwise logical XOR with 64 (bit 7
set, see vexpr), thus also covering code 127 (DEL),
which is mapped to 63 (question mark):
`? vexpr ^ 127 64'.

Whereas historically circumflex notation has often
been used for visualization purposes of control
codes, as in `^G', the reverse solidus notation has
been standardized: `\cG'. Some control codes also
have standardized (ISO-10646, ISO C) aliases, as
shown above (`\a', `\n', `\t' etc) : whenever such
an alias exists it will be used for display
purposes. The control code NUL (`\c@', a non-
standard extension) will suppress further output
for the remains of the token (which may extend
beyond the current quote), or, depending on the
context, the remains of all arguments for the
current command.
`\$NAME' Non-standard extension: expand the given variable
name, as above. Brace enclosing the name is
supported.
`\`{command}'
Not yet supported, just to raise awareness: Non-
standard extension.

Caveats:

? echo 'Quotes '${HOME}' and 'tokens" differ!"# no comment
? echo Quotes ${HOME} and tokens differ! # comment
? echo Don"'"t you worry$'\x21' The sun shines on us. $'\u263A'

Message list arguments

Many commands operate on message list specifications, as documented in
Specifying messages. The argument input is first split into individual
tokens via Shell-style argument quoting, which are then interpreted as
the mentioned specifications. If no explicit message list has been
specified, many commands will search for and use the next message
forward that satisfies the commands' requirements, and if there are no
messages forward of the current message, the search proceeds backwards;
if there are no good messages at all to be found, an error message is
shown and the command is aborted. The verbose output of the command
list will indicate whether a command searches for a default message, or
not.

Raw data arguments for codec commands

A special set of commands, which all have the string "codec" in their
name, like addrcodec, shcodec, urlcodec, take raw string data as input,
which means that the content of the command input line is passed
completely unexpanded and otherwise unchanged: like this the effect of
the actual codec is visible without any noise of possible shell quoting
rules etc., i.e., the user can input one-to-one the desired or
questionable data. To gain a level of expansion, the entire command
line can be evaluated first, for example

? vput shcodec res encode /usr/Sch"ones Wetter/heute.txt
? echo $res
$'/usr/Sch\u00F6nes Wetter/heute.txt'
? shcodec d $res
$'/usr/Sch\u00F6nes Wetter/heute.txt'
? eval shcodec d $res
/usr/Sch"ones Wetter/heute.txt

Filename transformations

Filenames, where expected, and unless documented otherwise, are
subsequently subject to the following filename transformations, in
sequence:

+o If the given name is a registered shortcut, it will be
replaced with the expanded shortcut. This step is mostly
taken for folders only.

+o The filename is matched against the following patterns or
strings. But for plus +file folder expansion this step is
mostly taken for folders only.

# (Number sign) is expanded to the previous file.
% (Percent sign) is replaced by the invoking user's
primary system mailbox, which either is the
(itself expandable) inbox if that is set, the
standardized absolute pathname indicated by MAIL
if that is set, or a built-in compile-time default
otherwise. When opening a folder the used name is
actively checked for being a primary mailbox,
first against inbox, then against MAIL.
%user Expands to the primary system mailbox of user (and
never the value of inbox, regardless of its actual
setting).
& (Ampersand) is replaced with the invoking user's
secondary mailbox, the MBOX.
+file Refers to a file in the folder directory (if that
variable is set).
%:filespec Expands to the same value as filespec, but has
special meaning when used with, for example, the
command folder: the file will be treated as a
primary system mailbox by, among others, the mbox
and save commands, meaning that messages that have
been read in the current session will be moved to
the MBOX mailbox instead of simply being flagged
as read.

+o Meta expansions may be applied to the resulting filename, as
allowed by the operation and applicable to the resulting
access protocol (also see On URL syntax and credential
lookup). For the file-protocol, a leading tilde `~'
character will be replaced by the expansion of HOME, except
when followed by a valid user name, in which case the home
directory of the given user is used instead.

A shell expansion as if specified in double-quotes (see
Shell-style argument quoting) may be applied, so that any
occurrence of `$VARIABLE' (or `${VARIABLE}') will be replaced
by the expansion of the variable, if possible; INTERNAL
VARIABLES as well as ENVIRONMENT (shell) variables can be
accessed through this mechanism.

Shell pathname wildcard pattern expansions (glob(7)) may be
applied as documented. If the fully expanded filename
results in multiple pathnames and the command is expecting
only one file, an error results.

In interactive context, in order to allow simple value
acceptance (via "ENTER"), arguments will usually be displayed
in a properly quoted form, so a file `diet\ is \curd.txt' may
be displayed as `'diet\ is \curd.txt''.

Commands

The following commands are available:

! Executes the SHELL command which follows, replacing
unescaped exclamation marks with the previously executed
command if the internal variable bang is set. This
command supports vput as documented in Command modifiers,
and manages the error number !. A 0 or positive exit
status ? reflects the exit status of the command, negative
ones that an error happened before the command was
executed, or that the program did not exit cleanly, but
maybe due to a signal: the error number is ^ERR-CHILD,
then.

In conjunction with the vput modifier the following
special cases exist: a negative exit status occurs if the
collected data could not be stored in the given variable,
which is a ^ERR-NOTSUP error that should otherwise not
occur. ^ERR-CANCELED indicates that no temporary file
could be created to collect the command output at first
glance. In case of catchable out-of-memory situations
^ERR-NOMEM will occur and S-nail will try to store the
empty string, just like with all other detected error
conditions.

# The comment-command causes the entire line to be ignored.
Note: this really is a normal command which' purpose is to
discard its arguments, not a "comment-start" indicating
special character, which means that for example trailing
comments on a line are not possible (except for commands
which use Shell-style argument quoting).

+ Goes to the next message in sequence and types it (like
"ENTER").

- Display the preceding message, or the n'th previous
message if given a numeric argument n.

= Shows the message number of the current message (the
"dot") when used without arguments, that of the given list
otherwise. Output numbers will be separated from each
other with the first character of ifs, and followed by the
first character of if-ws, if that is not empty and not
identical to the first. If that results in no separation
at all a space character is used. This command supports
vput (see Command modifiers), and manages the error number
!.

? [Option] Show a brief summary of commands. [Option] Given
an argument a synopsis for the command in question is
shown instead; commands can be abbreviated in general and
this command can be used to see the full expansion of an
abbreviation including the synopsis, try, for example
`?h', `?hel' and `?help' and see how the output changes.
To avoid that aliases are resolved the modifier \ can be
prepended to the argument, but note it must be quoted.
This mode also supports a more verbose output, which will
provide the information documented for list.

| A synonym for the pipe command.

account, unaccount
(ac, una) Creates, selects or lists (an) account(s).
Accounts are special incarnations of defined macros and
group commands and variable settings which together
usually arrange the environment for the purpose of
creating an email account. Different to normal macros
settings which are covered by localopts - here by default
enabled! - will not be reverted before the account is
changed again. The special account `null' (case-
insensitive) always exists, and all but it can be deleted
by the latter command, and in one operation with the
special name `*'. Also for all but it a possibly set
on-account-cleanup hook is called once they are left, also
for program exit.

Without arguments a listing of all defined accounts is
shown. With one argument the given account is activated:
the system inbox of that account will be activated (as via
folder), a possibly installed folder-hook will be run, and
the internal variable account will be updated. The two
argument form behaves identical to defining a macro as via
define. Important settings for accounts include folder,
from, hostname, inbox, mta, password and user (On URL
syntax and credential lookup), as well as things like
tls-config-pairs (Encrypted network communication), and
protocol specifics like imap-auth, pop3-auth, smtp-auth.

account myisp {
set folder=~/mail inbox=+syste.mbox record=+sent.mbox
set from='(My Name) myname@myisp.example'
set mta=smtp://mylogin@smtp.myisp.example
}

addrcodec Perform email address codec transformations on raw-data
argument, rather according to email standards (RFC 5322;
[v15 behaviour may differ] will furtherly improve).
Supports vput (see Command modifiers), and manages the
error number !. The first argument must be either
[+[+[+]]]e[ncode], d[ecode], s[kin] or skinl[ist] and
specifies the operation to perform on the rest of the
line.

Decoding will show how a standard-compliant MUA will
display the given argument, which should be an email
address. Please be aware that most MUAs have difficulties
with the address standards, and vary wildly when
(comments) in parenthesis, "double-quoted" strings, or
quoted-pairs, as below, become involved. [v15 behaviour
may differ] S-nail currently does not perform decoding
when displaying addresses.

Skinning is identical to decoding but only outputs the
plain address, without any string, comment etc.
components. Another difference is that it may fail with
the error number ! set to ^ERR-INVAL if decoding fails to
find a(n) (valid) email address, in which case the
unmodified input will be output again.

skinlist first performs a skin operation, and thereafter
checks a valid address for whether it is a registered
mailing list (see mlist and mlsubscribe), eventually
reporting that state in the error number ! as ^ERR-EXIST.
(This state could later become overwritten by an I/O
error, though.)

Encoding supports four different modes, lesser automated
versions can be chosen by prefixing one, two or three plus
signs: the standard imposes a special meaning on some
characters, which thus have to be transformed to so-called
quoted-pairs by pairing them with a reverse solidus `\' in
order to remove the special meaning; this might change
interpretation of the entire argument from what has been
desired, however! Specify one plus sign to remark that
parenthesis shall be left alone, two for not turning
double quotation marks into quoted-pairs, and three for
also leaving any user-specified reverse solidus alone.
The result will always be valid, if a successful exit
status is reported ([v15 behaviour may differ] the current
parser fails this assertion for some constructs). [v15
behaviour may differ] Addresses need to be specified in
between angle brackets `<', `>' if the construct becomes
more difficult, otherwise the current parser will fail; it
is not smart enough to guess right.

? addrc enc "Hey, you",<diet@exam.ple>\ out\ there
"\"Hey, you\", \\ out\\ there" <diet@exam.ple>
? addrc d "\"Hey, you\", \\ out\\ there" <diet@exam.ple>
"Hey, you", \ out\ there <diet@exam.ple>
? addrc s "\"Hey, you\", \\ out\\ there" <diet@exam.ple>
diet@exam.ple

alias, unalias
[Only new quoting rules](a, una) Define or list, and
remove, respectively, address aliases, which are a method
of creating personal distribution lists that map a single
name to none to multiple receivers, to be expanded after
Compose mode is left; the expansion correlates with metoo.
The latter command removes all given aliases, the special
name asterisk `*' will remove all existing aliases. When
used without arguments the former shows a list of all
currently known aliases, with one argument only the
target(s) of the given one. When given two arguments,
hyphen-minus `-' being the first, the target(s) of the
second is/are expanded recursively.

In all other cases the given alias is newly defined, or
will be appended to: arguments must either be themselves
valid alias names, or any other address type (see On
sending mail, and non-interactive mode). Recursive
expansion of aliases can be prevented by prefixing the
desired argument with the modifier reverse solidus \. A
valid alias name conforms to mta-aliases syntax, but
follow-up characters can also be the number sign `#',
colon `:', commercial at `@,' exclamation mark `!', period
`.' as well as "any character that has the high bit set".
The dollar sign `$' may be the last character. The number
sign `#' may need Shell-style argument quoting.

[v15 behaviour may differ] Unfortunately the colon is
currently not supported, as it interferes with normal
address parsing rules. [v15 behaviour may differ] Such
high bit characters will likely cause warnings at the
moment for the same reasons why colon is unsupported;
also, in the future locale dependent character set
validity checks will be performed.

? alias cohorts bill jkf mark kridle@ucbcory ~/cohorts.mbox
? alias mark mark@exam.ple
? set mta-aliases=/etc/aliases

alternates, unalternates
[Only new quoting rules] (alt) Manage a list of alternate
addresses or names of the active user, members of which
will be removed from recipient lists (except one). There
is a set of implicit alternates which is formed of the
values of LOGNAME, from, sender and reply-to. from will
not be used if sender is set. The latter command removes
the given list of alternates, the special name `*' will
discard all existing alternate names.

The former command manages the error number !. It shows
the current set of alternates when used without arguments;
in this mode only it also supports vput (see Command
modifiers). Otherwise the given arguments (after being
checked for validity) are appended to the list of
alternate names; in posix mode they replace that list
instead.

answered, unanswered
Take a message lists and mark each message as (not) having
been answered. Messages will be marked answered when
being replyd to automatically if the markanswered variable
is set. See the section Message states.

bind, unbind
[Option][Only new quoting rules] The bind command extends
the MLE (see On terminal control and line editor) with
freely configurable key bindings. The latter command
removes from the given context the given key binding, both
of which may be specified as a wildcard `*', so that
`unbind * *' will remove all bindings of all contexts.
Due to initialization order unbinding will not work for
built-in key bindings upon program startup, however:
please use line-editor-no-defaults for this purpose
instead.

With zero arguments, or with a context name the former
command shows all key bindings (of the given context; an
asterisk `*' will iterate over all contexts); a more
verbose listing will be produced if either of debug or
verbose are set. With two or more arguments a specific
binding is shown, or (re)established: the first argument
is the context to which the binding shall apply, the
second argument is a comma-separated list of the "keys"
which form the binding. Further arguments will be joined
to form the expansion, and cause the binding to be created
or updated. To indicate that a binding shall not be auto-
committed, but that the expansion shall instead be
furtherly editable by the user, a commercial at `@' (that
will be removed) can be placed last in the expansion, from
which leading and trailing whitespace will finally be
removed. Reverse solidus cannot be used as the last
character of expansion. An empty expansion will be
rejected.

Contexts define when a binding applies, i.e., a binding
will not be seen unless the context for which it is
defined for is currently active. This is not true for the
shared binding `base', which is the foundation for all
other bindings and as such always applies, its bindings,
however, only apply secondarily. The available contexts
are the shared `base', the `default' context which is used
in all not otherwise documented situations, and `compose',
which applies only to Compose mode.

Bindings are specified as a comma-separated list of byte-
sequences, where each list entry corresponds to one "key"
(press). Byte sequence boundaries will be forcefully
terminated after bind-inter-byte-timeout milliseconds,
whereas key sequences can be timed out via
bind-inter-key-timeout. A list entry may, indicated by a
leading colon character `:', also refer to the name of a
terminal capability; several dozen names are compiled in
and may be specified either by their terminfo(5), or, if
existing, by their termcap(5) name, regardless of the
actually used [Option]al terminal control library. But
any capability may be used, as long as the name is
resolvable by the [Option]al control library, or was
defined via the internal variable termcap. Input
sequences are not case-normalized, an exact match is
required to update or remove a binding. It is advisable
to use an initial escape or other control character (like
`\cA') for user (as opposed to purely terminal capability
based) bindings in order to avoid ambiguities; it also
reduces search time. Examples:

? bind base a,b echo one
? bind base $'\E',d mle-snarf-word-fwd # Esc(ape)
? bind base $'\E',$'\c?' mle-snarf-word-bwd # Esc,Delete
? bind default $'\cA',:khome,w 'echo Editable binding@'
? bind default a,b,c rm -irf / @ # Also editable
? bind default :kf1 File %
? bind compose :kf1 ~v

Note that the entire comma-separated list is first parsed
(over) as a shell-token with whitespace as the field
separator, then parsed and expanded for real with comma as
the field separator, therefore whitespace needs to be
properly quoted, see Shell-style argument quoting. Using
Unicode reverse solidus escape sequences renders a binding
defunctional if the locale does not support Unicode (see
Character sets), and using terminal capabilities does so
if no (corresponding) terminal control support is
(currently) available. Adding, deleting or modifying a
key binding invalidates the internal prebuilt lookup tree,
it will be recreated as necessary: this process will be
visualized in most verbose as well as in debug mode.

The following terminal capability names are built-in and
can be used in terminfo(5) or (if available) the two-
letter termcap(5) notation. See the respective manual for
a list of capabilities. The program infocmp(1) can be
used to show all the capabilities of TERM or the given
terminal type; using the -x flag will also show supported
(non-standard) extensions.

kbs or kb Backspace.
kdch1 or kD Delete character.
kDC or *4 -- shifted variant.
kel or kE Clear to end of line.
kext or @9 Exit.
kich1 or kI Insert character.
kIC or #3 -- shifted variant.
khome or kh Home.
kHOM or #2 -- shifted variant.
kend or @7 End.
knp or kN Next page.
kpp or kP Previous page.
kcub1 or kl Left cursor (with more modifiers: see
below).
kLFT or #4 -- shifted variant.
kcuf1 or kr Right cursor (ditto).
kRIT or %i -- shifted variant.
kcud1 or kd Down cursor (ditto).
kDN -- shifted variant (only terminfo).
kcuu1 or ku Up cursor (ditto).
kUP -- shifted variant (only terminfo).
kf0 or k0 Function key 0. Add one for each function
key up to kf9 and k9, respectively.
kf10 or k; Function key 10.
kf11 or F1 Function key 11. Add one for each
function key up to kf19 and F9,
respectively.

Some terminals support key-modifier combination
extensions, e.g., `Alt+Shift+xy'. For example, the delete
key, kdch1: in its shifted variant, the name is mutated to
kDC, then a number is appended for the states `Alt'
(kDC3), `Shift+Alt' (kDC4), `Control' (kDC5),
`Shift+Control' (kDC6), `Alt+Control' (kDC7), finally
`Shift+Alt+Control' (kDC8). The same for the left cursor
key, kcub1: KLFT, KLFT3, KLFT4, KLFT5, KLFT6, KLFT7,
KLFT8.

call [Only new quoting rules] Calls the given macro, which must
have been created via define (see there for more),
otherwise an ^ERR-NOENT error occurs. Calling macros
recursively will at some time excess the stack size limit,
causing a hard program abortion; if recursively calling a
macro is the last command of the current macro, consider
to use the command xcall, which will first release all
resources of the current macro before replacing the
current macro with the called one.

call_if Identical to call if the given macro has been created via
define, but does not fail nor warn if the macro does not
exist.

cd Synonym for chdir.

certsave [Option] Only applicable to S/MIME signed messages. Takes
an optional message list and a filename and saves the
certificates contained within the message signatures to
the named file in both human-readable and PEM format. The
certificates can later be used to send encrypted messages
to the respective message senders by setting
smime-encrypt-USER@HOST variables.

charsetalias, uncharsetalias
[Only new quoting rules] Manage alias mappings for
(conversion of) Character sets. Alias processing is not
performed for INTERNAL VARIABLES, for example
charset-8bit, and mappings are ineffective if character
set conversion is not available (features does not
announce `,+iconv,'). Expansion happens recursively for
cases where aliases point to other aliases (built-in loop
limit: 8).

The latter command deletes all aliases given as arguments,
or all at once when given the asterisk `*'. The former
shows the list of all currently defined aliases if used
without arguments, or the target of the given single
argument; when given two arguments, hyphen-minus `-' being
the first, the second is instead expanded recursively. In
all other cases the given arguments are treated as pairs
of character sets and their desired target alias name,
creating new or updating already existing aliases.

chdir [Only new quoting rules](ch) Change the working directory
to HOME or the given argument. Synonym for cd.

collapse, uncollapse
Only applicable to `thread'ed sort mode. Takes a message
list and makes all replies to these messages invisible in
header summaries, except for `new' messages and the "dot".
Also when a message with collapsed replies is displayed,
all of these are automatically uncollapsed. The latter
command undoes collapsing.

colour, uncolour
[Option][Only new quoting rules] Manage colour mappings of
and for a Coloured display. Without arguments the former
shows all currently defined mappings. Otherwise a colour
type is expected (case-insensitively), it must be one of
`256' for 256-colour terminals, `8', `ansi' or `iso' for
the standard 8-colour ANSI / ISO 6429 colour palette, and
`1' or `mono' for monochrome terminals, which only support
(some) font attributes. Without further arguments the
list of all currently defined mappings of the given type
is shown (here the special `all' or `*' also show all
currently defined mappings).

Otherwise the second argument defines the mappable slot,
the third argument a (comma-separated list of) colour and
font attribute specification(s), and the optionally
supported fourth argument can be used to specify a
precondition: if conditioned mappings exist they are
tested in (creation) order unless a (case-insensitive)
match has been found, and the default mapping (if any has
been established) will only be chosen as a last resort.
The types of available preconditions depend on the
mappable slot, the following of which exist:

Mappings prefixed with `mle-' are used for the [Option]al
built-in Mailx-Line-Editor (MLE, see On terminal control
and line editor) and do not support preconditions.

mle-position This mapping is used for the position
indicator that is visible when a line
cannot be fully displayed on the screen.
mle-prompt Used for the prompt.
mle-error Used for the occasionally appearing error
indicator that is joined onto prompt. [v15
behaviour may differ] Also used for error
messages written on standard error .

Mappings prefixed with `sum-' are used in header
summaries, and they all understand the preconditions `dot'
(the current message) and `older' for elder messages (only
honoured in conjunction with datefield-markout-older).

sum-dotmark This mapping is used for the "dotmark" that
can be created with the `%>' or `%<'
formats of the variable headline.
sum-header For the complete header summary line except
the "dotmark" and the thread structure.
sum-thread For the thread structure which can be
created with the `%i' format of the
variable headline.

Mappings prefixed with `view-' are used when displaying
messages.

view-from_ This mapping is used for so-called `From_'
lines, which are MBOX file format specific
header lines (also see mbox-rfc4155).
view-header For header lines. A comma-separated list
of headers to which the mapping applies may
be given as a precondition; if the
[Option]al regular expression support is
available then if any of the magic regular
expression characters is seen the
precondition will be evaluated as (an
extended) one.
view-msginfo For the introductional message info line.
view-partinfo For MIME part info lines.

The following (case-insensitive) colour definitions and
font attributes are understood, multiple of which can be
specified in a comma-separated list:

ft= a font attribute: `bold', `reverse' or `underline'.
It is possible (and often applicable) to specify
multiple font attributes for a single mapping.

fg= foreground colour attribute, in order (numbers 0 - 7)
`black', `red', `green', `brown', `blue', `magenta',
`cyan' or `white'. To specify a 256-colour mode a
decimal number colour specification in the range 0 to
255, inclusive, is supported, and interpreted as
follows:

0 - 7 the standard ISO 6429 colours, as above.
8 - 15 high intensity variants of the standard
colours.
16 - 231 216 colours in tuples of 6.
232 - 255 grayscale from black to white in 24 steps.

#!/bin/sh -
fg() { printf "\033[38;5;${1}m($1)"; }
bg() { printf "\033[48;5;${1}m($1)"; }
i=0
while [ $i -lt 256 ]; do fg $i; i=$(($i + 1)); done
printf "\033[0m\n"
i=0
while [ $i -lt 256 ]; do bg $i; i=$(($i + 1)); done
printf "\033[0m\n"

bg= background colour attribute (see fg= for possible
values).

The command uncolour will remove for the given colour type
(the special type `*' selects all) the given mapping; if
the optional precondition argument is given only the exact
tuple of mapping and precondition is removed. The special
name `*' will remove all mappings (no precondition
allowed), thus `uncolour * *' will remove all established
mappings.

commandalias, uncommandalias
[Only new quoting rules] Define or list, and remove,
respectively, command aliases. An (command)alias can be
used everywhere a normal command can be used, but always
takes precedence: any arguments that are given to the
command alias are joined onto the alias expansion, and the
resulting string forms the command line that is, in
effect, executed. The latter command removes all given
aliases, the special name asterisk `*' will remove all
existing aliases. When used without arguments the former
shows a list of all currently known aliases, with one
argument only the expansion of the given one.

With two or more arguments a command alias is defined or
updated: the first argument is the name under which the
remaining command line should be accessible, the content
of which can be just about anything. An alias may itself
expand to another alias, but to avoid expansion loops
further expansion will be prevented if an alias refers to
itself or if an expansion depth limit is reached.
Explicit expansion prevention is available via reverse
solidus \, one of the Command modifiers.

? commandalias xx
s-nail: `commandalias': no such alias: xx
? commandalias xx echo hello,
? commandalias xx
commandalias xx 'echo hello,'
? xx
hello,
? xx world
hello, world

Copy (C) Similar to copy, but copy the messages to a file named
after the local part of the sender of the first message
instead of taking a filename argument; outfolder is
inspected to decide on the actual storage location.

copy (c) Copy messages to the named file and do not mark them
as being saved; otherwise identical to save.

csop [Only new quoting rules] A multiplexer command which
provides C-style string operations on 8-bit bytes without
a notion of locale settings and character sets,
effectively assuming ASCII data. For numeric and other
operations refer to vexpr. vput, one of the Command
modifiers, is supported. The error result is `-1' for
usage errors and numeric results, the empty string
otherwise; missing data errors, as for unsuccessful
searches, result in the ! error number being set to
^ERR-NODATA. Where the question mark `?' modifier suffix
is supported, a case-insensitive (ASCII mapping) operation
mode is supported; the keyword `case' is optional so that
`find?' and `find?case' are identical.

length Queries the length of the given argument.

hash, hash32 Calculates a hash value of the given
argument. The latter will return a 32-bit
result regardless of host environment. `?'
modifier suffix is supported. These use
Chris Torek's hash algorithm, the resulting
hash value is bit mixed as shown by Bret
Mulvey.

find Search for the second in the first
argument. Shows the resulting 0-based
offset shall it have been found. `?'
modifier suffix is supported.

substring Creates a substring of its first argument.
The optional second argument is the 0-based
starting offset, a negative one counts from
the end; the optional third argument
specifies the length of the desired result,
a negative length leaves off the given
number of bytes at the end of the original
string; by default the entire string is
used. This operation tries to work around
faulty arguments (set verbose for error
logs), but reports them via the error
number ! as ^ERR-OVERFLOW.

trim Trim away whitespace characters from both
ends of the argument.

trim-front Trim away whitespace characters from the
begin of the argument.

trim-end Trim away whitespace characters from the
end of the argument.

cwd Show the name of the current working directory, as
reported by getcwd(3). Supports vput (see Command
modifiers). The return status is tracked via ?.

Decrypt [Option] For unencrypted messages this command is
identical to Copy; Encrypted messages are first decrypted,
if possible, and then copied.

decrypt [Option] For unencrypted messages this command is
identical to copy; Encrypted messages are first decrypted,
if possible, and then copied.

define, undefine
The latter command deletes the given macro, the special
name `*' will discard all existing macros. Deletion of
(a) macro(s) can be performed from within running (a)
macro(s), including self-deletion. Without arguments the
former command prints the current list of macros,
including their content, otherwise it defines a macro,
replacing an existing one of the same name as applicable.

A defined macro can be invoked explicitly by using the
call, call_if and xcall commands, or implicitly if a macro
hook is triggered, for example a folder-hook. Execution
of a macro body can be stopped from within by calling
return.

Temporary macro block-scope variables can be created or
deleted with the local command modifier in conjunction
with the commands set and unset, respectively. To enforce
unrolling of changes made to (global) INTERNAL VARIABLES
the command localopts can be used instead; its covered
scope depends on how (i.e., "as what": normal macro,
folder hook, hook, account switch) the macro is invoked.

Inside a called macro, the given positional parameters are
implicitly local to the macro's scope, and may be accessed
via the variables *, @, # and 1 and any other positive
unsigned decimal number less than or equal to #.
Positional parameters can be shifted, or become completely
replaced, removed etc. via vpospar. A helpful command for
numeric computation and string evaluations is vexpr, csop
offers C-style byte string operations.

define name {
command1
command2
...
commandN
}

define exmac {
echo Parameter 1 of ${#} is ${1}, all: ${*} / ${@}
return 1000 0
}
call exmac Hello macro exmac!
echo ${?}/${!}/${^ERRNAME}

delete, undelete
(d, u) Marks the given message list as being or not being
`deleted', respectively; if no argument has been specified
then the usual search for a visible message is performed,
as documented for Message list arguments, showing only the
next input prompt if the search fails. Deleted messages
will neither be saved in the secondary mailbox MBOX nor
will they be available for most other commands. If the
autoprint variable is set, the new "dot" or the last
message restored, respectively, is automatically typed;
also see dp, dt.

digmsg [Only new quoting rules] Digging (information out of)
messages is possible through digmsg objects, which can be
created for the given message number; in Compose mode the
hyphen-minus `-' will instead open the message that is
being composed. If a hyphen-minus is given as the
optional third argument then output will be generated on
the standard output channel instead of being subject to
consumption by the readall (or read and readsh)
command(s). Note: output must be consumed before normal
processing can continue; for digmsg objects this means
each command output has to be read until the end of file
(EOF) state occurs.

The objects may be removed again by giving the same
identifier used for creation; this step could be omitted:
objects will be automatically closed when the active
folder (mailbox) or the compose mode is left,
respectively. In all other use cases the second argument
is an object identifier, and the third and all following
arguments are interpreted as via ~^ (see COMMAND ESCAPES):

? vput = msgno; digmsg create $msgno
? digmsg $msgno header list; readall x; echon $x
210 Subject From To Message-ID References In-Reply-To
? digmsg $msgno header show Subject;readall x;echon $x
212 Subject
'Hello, world'

? digmsg remove $msgno

discard (di) Identical to ignore. Superseded by the multiplexer
headerpick.

dp, dt Delete the given messages and automatically type the new
"dot" if one exists, regardless of the setting of
autoprint.

dotmove Move the "dot" up or down by one message when given `+' or
`-' argument, respectively.

draft, undraft
Take message lists and mark each given message as being
draft, or not being draft, respectively, as documented in
the section Message states.

echo [Only new quoting rules](ec) Print the given strings,
equivalent to the shell utility echo(1), that is, Shell-
style argument quoting expansion is performed and,
different to the otherwise identical echon, a trailing
newline is echoed. vput as documented in Command
modifiers is supported, and the error number ! is managed:
if data is stored in a variable then the return value
reflects the length of the result string in case of
success and is `-1' on error.

Remarks: this command traditionally (in BSD Mail) also
performed Filename transformations, which is standard
incompatible and hard to handle because quoting
transformation patterns is not possible; the subcommand
file-expand of vexpr can be used to expand filenames.

echoerr [Only new quoting rules] Identical to echo, but the
message is written to standard error, and prefixed by
log-prefix. Also see echoerrn. In interactive sessions
the [Option]al message ring queue for errors will be used
instead, if available and vput was not used.

echon [Only new quoting rules] Identical to echo, but does not
write or store a trailing newline.

echoerrn [Only new quoting rules] Identical to echoerr, but does
not write or store a trailing newline.

edit (e) Point the text EDITOR at each message from the given
list in turn. Modified contents are discarded unless the
writebackedited variable is set, and are not used unless
the mailbox can be written to and the editor returns a
successful exit status. visual can be used instead for a
more display oriented editor.

elif Part of the if (see there for more), elif, else, endif
conditional -- if the condition of a preceding if was
false, check the following condition and execute the
following block if it evaluates true.

else (el) Part of the if (see there for more), elif, else,
endif conditional -- if none of the conditions of the
preceding if and elif commands was true, the else block is
executed.

endif (en) Marks the end of an if (see there for more), elif,
else, endif conditional execution block.

environ [Only new quoting rules] There is a strict separation in
between INTERNAL VARIABLES and the program ENVIRONMENT,
which is inherited by child processes. Some variables of
the latter are however vivid for program operation, their
purpose is known, therefore they have been integrated
transparently into handling of the former, as accessible
via set and unset. To integrate any other environment
variable, and/or to export internal variables into the
process environment where they normally are not, a link
needs to become established with this command, for example

environ link PERL5LIB TZ

Afterwards changing such variables with set will cause
automatic updates of the environment, too. Sufficient
system support provided (it was in BSD as early as 1987,
and is standardized since Y2K) removing such variables
with unset will remove them also from the environment, but
in any way the knowledge they ever have been linked will
be lost. This implies that localopts may cause loss of
such links.

The subcommand unlink removes an existing link without
otherwise touching variables, the set and unset
subcommands are identical to set and unset, but
additionally update the program environment accordingly;
removing a variable breaks any freely established link.

errors [Option] As console user interfaces at times scroll error
messages by too fast and/or out of scope, data can
additionally be sent to an error queue manageable by this
command: show or no argument will display and clear the
queue, clear will only clear it. As the queue becomes
filled with errors-limit entries the eldest entries are
being dropped. There are also the variables
^ERRQUEUE-COUNT and ^ERRQUEUE-EXISTS.

eval [Only new quoting rules] Construct a command by
concatenating the arguments, separated with a single space
character, and then evaluate the result. This command
passes through the exit status ? and error number ! of the
evaluated command; also see call.

define xxx {
echo "xxx arg <$1>"
shift
if $# -gt 0
\xcall xxx "$@"
endif
}
define yyy {
eval "$@ ' ball"
}
call yyy '\call xxx' "b\$'\t'u ' "
call xxx arg <b u>
call xxx arg < >
call xxx arg <ball>

exit (ex or x) Exit from S-nail without changing the active
mailbox and skip any saving of messages in the secondary
mailbox MBOX, as well as a possibly tracked line editor
history-file. A possibly set on-account-cleanup will be
invoked, however. The optional status number argument
will be passed through to exit(3). [v15 behaviour may
differ] For now it can happen that the given status will
be overwritten, later this will only occur if a later
error needs to be reported onto an otherwise success
indicating status.

File (Fi) Like folder, but open the mailbox read-only.

file (fi) See folder.

filetype, unfiletype
[Only new quoting rules] Define, list, and remove,
respectively, file handler hooks, which provide (shell)
commands that enable S-nail to load and save MBOX files
from and to files with the registered file extensions, as
shown and described for folder. The extensions are used
case-insensitively, yet the auto-completion feature of for
example folder will only work case-sensitively. An
intermediate temporary file will be used to store the
expanded data. The latter command will remove hooks for
all given extensions, asterisk `*' will remove all
existing handlers.

When used without arguments the former shows a list of all
currently defined file hooks, with one argument the
expansion of the given alias. Otherwise three arguments
are expected, the first specifying the file extension for
which the hook is meant, and the second and third defining
the load- and save commands to deal with the file type,
respectively, both of which must read from standard input
and write to standard output. Changing hooks will not
affect already opened mailboxes ([v15 behaviour may
differ] except below). [v15 behaviour may differ] For now
too much work is done, and files are oftened read in twice
where once would be sufficient: this can cause problems if
a filetype is changed while such a file is opened; this
was already so with the built-in support of .gz etc. in
Heirloom, and will vanish in v15. [v15 behaviour may
differ] For now all handler strings are passed to the
SHELL for evaluation purposes; in the future a `!' prefix
to load and save commands may mean to bypass this shell
instance: placing a leading space will avoid any possible
misinterpretations.

? filetype bz2 'bzip2 -dc' 'bzip2 -zc' \
gz 'gzip -dc' 'gzip -c' xz 'xz -dc' 'xz -zc' \
zst 'zstd -dc' 'zstd -19 -zc' \
zst.pgp 'gpg -d | zstd -dc' 'zstd -19 -zc | gpg -e'
? set record=+sent.zst.pgp

flag, unflag
Take message lists and mark the messages as being flagged,
or not being flagged, respectively, for urgent/special
attention. See the section Message states.

Folder (Fold) Like folder, but open the mailbox read-only.

folder (fold) Open a new, or show status information of the
current mailbox. If an argument is given, changes (such
as deletions) will be written out, a new mailbox will be
opened, the internal variables mailbox-resolved and
mailbox-display will be updated, a set according
folder-hook is executed, and optionally a summary of
headers is displayed if the variable header is set.

Filename transformations will be applied to the name
argument, and `protocol://' prefixes are, i.e., URL (see
On URL syntax and credential lookup) syntax is understood,
as in `mbox:///tmp/somefolder'. If a protocol prefix is
used the mailbox type is fixated, otherwise opening none-
existing folders uses the protocol defined in newfolders.

For the protocols mbox and file (MBOX database), as well
as eml (electronic mail message [v15 behaviour may differ]
read-only) the list of all registered filetypes is
traversed to check whether hooks shall be used to load
(and save) data from (and to) the given name. Changing
hooks will not affect already opened mailboxes. For
example, the following creates hooks for the gzip(1)
compression tool and a combined compressed and encrypted
format:

? filetype \
gzip 'gzip -dc' 'gzip -c' \
zst.pgp 'gpg -d | zstd -dc' 'zstd -19 -zc | gpg -e'

For historic reasons filetypes provide limited (case-
sensitive) auto-completion capabilities. For example
`mbox.gz' will be found for `? file mbox', provided that
corresponding handlers are installed. It will neither
find `mbox.GZ' nor `mbox.Gz' however, but an explicit `?
file mbox.GZ' will find and use the handler for `gz'.
[v15 behaviour may differ] The latter mode can only be
used for MBOX files.

EML files consist of only one mail message, [v15 behaviour
may differ] and can only be opened read-only. When
reading MBOX files tolerant POSIX rules are used by
default. Invalid message boundaries that can be found
quite often in historic MBOX files will be complained
about (even more with debug): in this case the method
described for mbox-rfc4155 can be used to create a valid
MBOX database from the invalid input.

MBOX databases and EML files will always be protected via
file-region locks (fcntl(2)) during file operations to
protect against concurrent modifications. [Option] An
MBOX inbox (MAIL) or primary system mailbox will also be
protected by so-called dotlock files, the traditional way
of mail spool file locking: for any file `x' a lock file
`x.lock' will be created during the synchronization, in
the same directory and with the same user and group
identities as the file of interest -- as necessary created
by an external privileged dotlock helper. dotlock-disable
disables dotlock files. Also see FAQ: Howto handle stale
dotlock files.

[Option] If no protocol has been fixated, and name refers
to a directory with the subdirectories `tmp', `new' and
`cur', then it is treated as a folder in "Maildir" format.
The maildir format stores each message in its own file,
and has been designed so that file locking is not
necessary when reading or writing files.

[Option]ally URLs can be used to access network resources,
securely via Encrypted network communication, if so
supported. Network communication socket timeouts are
configurable via socket-connect-timeout. All network
traffic may be proxied over a SOCKS server via
socks-proxy.

[v15-compat]
protocol://[user[:password]@]host[:port][/path]
[no v15-compat] protocol://[user@]host[:port][/path]

[Option]ally supported network protocols are pop3 (POP3)
and pop3s (POP3 with TLS encrypted transport), imap and
imaps. The [/path] part is valid only for IMAP; there it
defaults to INBOX. Network URLs require a special
encoding as documented in the section On URL syntax and
credential lookup.

folders Lists the names of all folders below the given argument or
folder. For file-based protocols LISTER will be used for
display purposes.

Followup, followup
(Compose mode)(F,fo) Similar to Reply, and reply,
respectively, but save the message in a file named after
the local part of the (first) recipient's address,
possibly overwriting record, and honouring outfolder.
Also see Copy and Save.

Forward (Compose mode) Similar to forward, but saves the message
in a file named after the local part of the recipient's
address (instead of in record).

forward (Compose mode) Take a message list and the address of a
recipient, subject to fullnames, to whom the messages are
sent. The text of the original message is included in the
new one, enclosed by the values of forward-inject-head and
forward-inject-tail.
content-description-forwarded-message is inspected. The
list of included headers can be filtered with the
`forward' slot of the white- and blacklisting command
headerpick. Only the first part of a multipart message is
included but for forward-as-attachment.

This may generate the errors ^ERR-DESTADDRREQ if no
receiver has been specified, or was rejected by expandaddr
policy, ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a
necessary character set conversion fails, and ^ERR-INVAL
for other errors. It can also fail with errors of
Specifying messages. Any error stops processing of
further messages.

from (f) Takes a list of message specifications and displays a
summary of their message headers, exactly as via headers,
making the first message of the result the new "dot" (the
last message if showlast is set). An alias of this
command is search. Also see Specifying messages.

Fwd [Obsolete] Alias for Forward.

fwd [Obsolete] Alias for forward.

fwdignore [Obsolete] Superseded by the multiplexer headerpick.

fwdretain [Obsolete] Superseded by the multiplexer headerpick.

ghost, unghost
[Obsolete] Replaced by commandalias, uncommandalias.

headerpick, unheaderpick
[Only new quoting rules] Multiplexer command to manage
white- and blacklisting selections of header fields for a
variety of applications. Without arguments the set of
contexts that have settings is displayed. When given
arguments, the first argument is the context to which the
command applies, one of (case-insensitive) `type' for
display purposes (for example type), `save' for selecting
which headers shall be stored persistently when save,
copy, move or even decrypting messages (note that MIME
related etc. header fields should not be ignored in order
to not destroy usability of the message in this case),
`forward' for stripping down messages when forwarding
message (has no effect if forward-as-attachment is set),
and `top' for defining user-defined set of fields for the
command top.

The current settings of the given context are displayed if
it is the only argument. A second argument denotes the
type of restriction that is to be chosen, it may be (a
case-insensitive prefix of) `retain' or `ignore' for
white- and blacklisting purposes, respectively.
Establishing a whitelist suppresses inspection of the
corresponding blacklist.

If no further argument is given the current settings of
the given type will be displayed, otherwise the remaining
arguments specify header fields, which [Option]ally may be
given as regular expressions, to be added to the given
type. The special wildcard field (asterisk, `*') will
establish a (fast) shorthand setting which covers all
fields.

The latter command always takes three or more arguments
and can be used to remove selections, i.e., from the given
context, the given type of list, all the given headers
will be removed, the special argument `*' will remove all
headers.

headers (h) Show the current group of headers, the size of which
depends on the variable screen in interactive mode, and
the format of which can be defined with headline. If a
message-specification is given the group of headers
containing the first message therein is shown and the
message at the top of the screen becomes the new "dot";
the last message is targeted if showlast is set.

help (hel) A synonym for ?.

history [Option] Without arguments or when given show all history
entries are shown (this mode also supports a more verbose
output). load will replace the list of entries with the
content of history-file, and save will dump all entries to
said file, replacing former content, and clear will delete
all entries. The argument can also be a signed decimal
NUMBER, which will select and evaluate the respective
history entry, and move it to the top of the history; a
negative number is used as an offset to the current
command so that `-1' will select the last command, the
history top, whereas delete will delete all given entries
(:NUMBER:). Also see On terminal control and line editor.

hold (ho, also preserve) Takes a message list and marks each
message therein to be saved in the user's system inbox
instead of in the secondary mailbox MBOX. Does not
override the delete command. S-nail deviates from the
POSIX standard with this command, because a next command
issued after hold will display the following message, not
the current one.

if (i) Part of the if, elif, else, endif conditional
execution construct -- if the given condition is true then
the encapsulated block is executed. The POSIX standard
only supports the (case-insensitive) conditions `r'eceive
and `s'end, the remaining are non-portable extensions.
[v15 behaviour may differ] In conjunction with the wysh
command prefix(es) Shell-style argument quoting and more
test operators are available.

if receive
commands ...
else
commands ...
endif

Further (case-insensitive) one-argument conditions are
`t'erminal which evaluates to true in interactive terminal
sessions (running with standard input or standard output
attached to a terminal, and none of the "quickrun" command
line options -e, -H and -L have been used), as well as any
boolean value (see INTERNAL VARIABLES for textual boolean
representations) to mark an enwrapped block as "never
execute" or "always execute". (Remarks: condition syntax
errors skip all branches until endif.)

[no v15-compat] and without wysh: It is possible to check
INTERNAL VARIABLES as well as ENVIRONMENT variables for
existence or compare their expansion against a user given
value or another variable by using the `$' ("variable
next") conditional trigger character; a variable on the
right hand side may be signalled using the same mechanism.
Variable names may be enclosed in a pair of matching
braces. When this mode has been triggered, several
operators are available ([v15-compat] and wysh: they are
always available, and there is no trigger: variables will
have been expanded by the shell-compatible parser before
the if etc. command sees them).

[v15-compat] Two argument conditions. Variables can be
tested for existence and expansion: `-N' will test whether
the given variable exists, so that `-N editalong' will
evaluate to true when editalong is set, whereas `-Z
editalong' will if it is not. `-n "$editalong"' will be
true if the variable is set and expands to a non-empty
string, `-z $'\$editalong'' only if the expansion is
empty, whether the variable exists or not. The remaining
conditions take three arguments.

Integer operators treat the arguments on the left and
right hand side of the operator as integral numbers and
compare them arithmetically. It is an error if any of the
operands is not a valid integer, an empty argument (which
implies it had been quoted) is treated as if it were 0.
Via the question mark `?' modifier suffix a saturated
operation mode is available where numbers will linger at
the minimum or maximum possible value, instead of
overflowing (or trapping), the keyword `saturated' is
optional, `==?', `==?satu' and `==?saturated' are
therefore identical. Available operators are `-lt' (less
than), `-le' (less than or equal to), `-eq' (equal), `-ne'
(not equal), `-ge' (greater than or equal to), and `-gt'
(greater than).

String and regular expression data operators compare the
left and right hand side according to their textual
content. Unset variables are treated as the empty string.
Via the question mark `?' modifier suffix a case-
insensitive operation mode is available, the keyword
`case' is optional, `==?' and `==?case' are identical.

Available string operators are `<' (less than), `<=' (less
than or equal to), `==' (equal), `!=' (not equal), `>='
(greater than or equal to), `>' (greater than), `=%' (is
substring of) and `!%' (is not substring of). By default
these operators work on bytes and (therefore) do not take
into account character set specifics. If the case-
insensitivity modifier has been used, case is ignored
according to the rules of the US-ASCII encoding, i.e.,
bytes are still compared.

When the [Option]al regular expression support is
available, the additional string operators `=~' and `!~'
can be used. They treat the right hand side as an
extended regular expression that is matched according to
the active locale (see Character sets), i.e., character
sets should be honoured correctly.

Conditions can be joined via AND-OR lists (where the AND
operator is `&&' and the OR operator is `||'), which have
equal precedence and will be evaluated with left
associativity, thus using the same syntax that is known
for the sh(1). It is also possible to form groups of
conditions and lists by enclosing them in pairs of
brackets `[ ... ]', which may be interlocked within each
other, and also be joined via AND-OR lists.

The results of individual conditions and entire groups may
be modified via unary operators: the unary operator `!'
will reverse the result.

wysh set v15-compat=yes # with value: automatic "wysh"!
if -N debug;echo *debug* set;else;echo not;endif
if "$ttycharset" == UTF-8 || "$ttycharset" ==?cas UTF8
echo ttycharset is UTF-8, the former case-sensitive!
endif
set t1=one t2=one
if [ "${t1}" == "${t2}" ]
echo These two variables are equal
endif
if "$features" =% ,+regex, && "$TERM" =~?case ^xterm.*
echo ..in an X terminal
endif
if [ [ true ] && [ [ "${debug}" != '' ] || \
[ "$verbose" != '' ] ] ]
echo Noisy, noisy
endif
if true && [ -n "$debug" || -n "${verbose}" ]
echo Left associativity, as is known from the shell
endif

ignore (ig) Identical to discard. Superseded by the multiplexer
headerpick.

list Shows the names of all available commands, in command
lookup order. [Option] In conjunction with a set variable
verbose additional information will be provided for each
command: the argument type will be indicated, the
documentation string will be shown, and the set of command
flags will show up:

``local'' command supports the command modifier
local.
``vput'' command supports the command modifier
vput.
`*!*' the error number is tracked in !.
`needs-box' whether the command needs an active
mailbox, a folder.
`ok:' indicators whether command is ...
`batch/interactive'
usable in interactive
or batch mode (-#).
`send-mode' usable in send mode.
`subprocess' allowed to be used
when running in a
subprocess instance,
for example from
within a macro that
is called via
on-compose-splice.
`not ok:' indicators whether command is not ...
`compose mode' available in
Compose mode.
`startup' available during
program startup,
like in Resource
files.
`gabby' The command produces history-gabby
history entries.

localopts Enforce change localization of environ (linked)
ENVIRONMENT as well as (global) INTERNAL VARIABLES,
meaning that their state will be reverted to the former
one once the "covered scope" is left. Just like the
command modifier local, which provides block-scope
localization for some commands (instead), it can only be
used inside of macro definition blocks introduced by
account or define. The covered scope of an account is
left once a different account is activated, and some
macros, notably folder-hooks, use their own specific
notion of covered scope, here it will be extended until
the folder is left again.

This setting stacks up: i.e., if `macro1' enables change
localization and calls `macro2', which explicitly resets
localization, then any value changes within `macro2' will
still be reverted when the scope of `macro1' is left.
(Caveats: if in this example `macro2' changes to a
different account which sets some variables that are
already covered by localizations, their scope will be
extended, and in fact leaving the account will (thus)
restore settings in (likely) global scope which actually
were defined in a local, macro private context!)

This command takes one or two arguments, the optional
first one specifies an attribute that may be one of scope,
which refers to the current scope and is thus the default,
call, which causes any macro that is being called to be
started with localization enabled by default, as well as
call-fixate, which (if enabled) disallows any called macro
to turn off localization: like this it can be ensured that
once the current scope regains control, any changes made
in deeper levels have been reverted. The latter two are
mutually exclusive, and neither affects xcall. The
(second) argument is interpreted as a boolean (string, see
INTERNAL VARIABLES) and states whether the given attribute
shall be turned on or off.

define temporary_settings {
set possibly_global_option1
localopts on
set localized_option1
set localized_option2
localopts scope off
set possibly_global_option2
}

Lfollowup, Lreply
(Compose mode) Reply to messages that come in via known
(mlist) or subscribed (mlsubscribe) mailing lists, or
pretend to do so (see Mailing lists): on top of the usual
followup and reply, respectively, functionality this will
actively resort and even remove message recipients in
order to generate a message that is supposed to be sent to
a mailing list. For example it will also implicitly
generate a `Mail-Followup-To:' header if that seems
useful, regardless of the setting of the variable
followup-to. For more documentation please refer to On
sending mail, and non-interactive mode.

This may generate the errors ^ERR-DESTADDRREQ if no
receiver has been specified, ^ERR-PERM if some addressees
where rejected by expandaddr, ^ERR-IO if an I/O error
occurs, ^ERR-NOTSUP if a necessary character set
conversion fails, and ^ERR-INVAL for other errors. It can
also fail with errors of Specifying messages. Occurrence
of some of the errors depend on the value of expandaddr.
Any error stops processing of further messages.

Mail (Compose mode) Similar to mail, but saves the message in a
file named after the local part of the first recipient's
address (instead of in record).

mail (Compose mode)(m) Takes a (list of) recipient address(es)
as (an) argument(s), or asks on standard input if none
were given; then collects the remaining mail content and
sends it out. Unless the internal variable fullnames is
set recipient addresses will be stripped from comments,
names etc. For more documentation please refer to On
sending mail, and non-interactive mode.

This may generate the errors ^ERR-DESTADDRREQ if no
receiver has been specified, ^ERR-PERM if some addressees
where rejected by expandaddr, ^ERR-NOTSUP if multiple
messages have been specified, ^ERR-IO if an I/O error
occurs, ^ERR-NOTSUP if a necessary character set
conversion fails, and ^ERR-INVAL for other errors. It can
also fail with errors of Specifying messages. Occurrence
of some of the errors depend on the value of expandaddr.

mailcap [Option] When used without arguments or if show has been
given the content of The Mailcap files cache is shown,
(re-)initializing it first (as necessary. If the argument
is load then the cache will only be (re-)initialized, and
clear will remove its contents. Note that S-nail will try
to load the files only once, use `mailcap clear' to unlock
further attempts. Loading and parsing can be made more
verbose.

mbox (mb) The given message list is to be sent to the secondary
mailbox MBOX when S-nail is quit; this is the default
action unless the variable hold is set. [v15 behaviour
may differ] This command can only be used in a primary
system mailbox.

mimetype, unmimetype
[Only new quoting rules] Without arguments the content of
the MIME type cache will displayed; a more verbose listing
will be produced if either of debug or verbose are set.
When given arguments they will be joined, interpreted as
shown in The mime.types files (also see HTML mail and MIME
attachments), and the resulting entry will be added
(prepended) to the cache. In any event MIME type sources
are loaded first as necessary - mimetypes-load-control can
be used to fine-tune which sources are actually loaded.

The latter command deletes all specifications of the given
MIME type, thus `? unmimetype text/plain' will remove all
registered specifications for the MIME type `text/plain'.
The special name `*' will discard all existing MIME types,
just as will `reset', but which also reenables cache
initialization via mimetypes-load-control.

mimeview [v15 behaviour may differ] Only available in interactive
mode, this command allows execution of external MIME type
handlers which do not integrate into the normal type
output (see HTML mail and MIME attachments). ([v15
behaviour may differ] No syntax to directly address parts,
this restriction may vanish.) The user will be asked for
each non-text part of the given message in turn whether
the registered handler shall be used to display the part.

mlist, unmlist
[Only new quoting rules] Manage the list of known Mailing
lists; subscriptions are controlled via mlsubscribe. The
latter command deletes all given arguments, or all at once
when given the asterisk `*'. The former shows the list of
all currently known lists if used without arguments,
otherwise the given arguments will become known. [Option]
In the latter case, arguments which contain any of the
magic regular expression characters will be interpreted as
one, possibly matching many addresses; these will be
sequentially matched via linked lists instead of being
looked up in a dictionary.

mlsubscribe, unmlsubscribe
Building upon the command pair mlist, unmlist, but only
managing the subscription attribute of mailing lists.
(The former will also create not yet existing mailing
lists.)

Move Similar to move, but move the messages to a file named
after the local part of the sender of the first message
instead of taking a filename argument; outfolder is
inspected to decide on the actual storage location.

move Acts like copy but marks the messages for deletion if they
were transferred successfully.

More Like more, but also displays header fields which would not
pass the headerpick selection, and all MIME parts.
Identical to Page.

more Invokes the PAGER on the given messages, even in non-
interactive mode and as long as the standard output is a
terminal. Identical to page.

mtaaliases [Option] When used without arguments or if show has been
given the content of the mta-aliases cache is shown,
(re-)initializing it first (as necessary). If the
argument is load then the cache will only be
(re-)initialized, and clear will remove its contents.

netrc [Option] When used without arguments, or when the argument
was show the content of the ~/:.netrc cache is shown,
initializing it as necessary. If the argument is load
then the cache will be (re)loaded, whereas clear removes
it. Loading and parsing can be made more verbose. lookup
will query the cache for the URL given as the second
argument (`[USER@]HOST'). See netrc-lookup, netrc-pipe
and the section On URL syntax and credential lookup; the
section The .netrc file documents the file format in
detail.

newmail Checks for new mail in the current folder without
committing any changes before. If new mail is present, a
message is shown. If the header variable is set, the
headers of each new message are also shown. This command
is not available for all mailbox types.

next (n) (like `+' or "ENTER") Goes to the next message in
sequence and types it. With an argument list, types the
next matching message.

New Same as Unread.

new Same as unread.

noop If the current folder is accessed via a network
connection, a "NOOP" command is sent, otherwise no
operation is performed.

Page Like page, but also displays header fields which would not
pass the headerpick selection, and all MIME parts.
Identical to More.

page Invokes the PAGER on the given messages, even in non-
interactive mode and as long as the standard output is a
terminal. Identical to more.

Pipe Like pipe but also pipes header fields which would not
pass the headerpick selection, and all parts of MIME
`multipart/alternative' messages.

pipe (pi) Takes an optional message list and shell command
(that defaults to cmd), and pipes the messages through the
command. If the page variable is set, every message is
followed by a formfeed character.

preserve (pre) A synonym for hold.

Print (P) Alias for Type.

print (p) Research UNIX equivalent of type.

quit (q) Terminates the session, saving all undeleted, unsaved
messages in the current secondary mailbox MBOX, preserving
all messages marked with hold or preserve or never
referenced in the system inbox, and removing all other
messages from the primary system mailbox. If new mail has
arrived during the session, the message "You have new
mail" will be shown. If given while editing a mailbox
file with the command line option -f, then the edit file
is rewritten. A return to the shell is effected, unless
the rewrite of edit file fails, in which case the user can
escape with the exit command. The optional status number
argument will be passed through to exit(3). [v15
behaviour may differ] For now it can happen that the given
status will be overwritten, later this will only occur if
a later error needs to be reported onto an otherwise
success indicating status.

read [Only new quoting rules] Read a line from standard input,
or the channel set active via readctl, and assign the
data, which will be split as indicated by ifs, to the
given variables. The variable names are checked by the
same rules as documented for vput, and the same error
codes will be seen in !; the exit status ? indicates the
number of bytes read, it will be `-1' with the error
number ! set to ^ERR-BADF in case of I/O errors, or
^ERR-NONE upon End-Of-File. If there are more fields than
variables, assigns successive fields to the last given
variable. If there are less fields than variables,
assigns the empty string to the remains.

? read a b c
H e l l o
? echo "<$a> <$b> <$c>"
<H> <e> <l l o>
? wysh set ifs=:; read a b c;unset ifs
hey2.0,:"'you ",:world!:mars.:
? echo $?/$^ERRNAME / <$a><$b><$c>
0/NONE / <hey2.0,><"'you ",><world!:mars.:><><>

readsh [Only new quoting rules] Like read, but splits on shell
token boundaries (see Shell-style argument quoting) rather
than at ifs. [v15 behaviour may differ] Could become a
commandalias, maybe `read --tokenize --'.

readall [Only new quoting rules] Read anything from standard
input, or the channel set active via readctl, and assign
the data to the given variable. The variable name is
checked by the same rules as documented for vput, and the
same error codes will be seen in !; the exit status ?
indicates the number of bytes read, it will be `-1' with
the error number ! set to ^ERR-BADF in case of I/O errors,
or ^ERR-NONE upon End-Of-File. [v15 behaviour may differ]
The input data length is restricted to 31-bits.

readctl [Only new quoting rules] Manages input channels for read,
readsh and readall, to be used to avoid complicated or
impracticable code, like calling read from within a macro
in non-interactive mode. Without arguments, or when the
first argument is show, a listing of all known channels is
printed. Channels can otherwise be created, and existing
channels can be set active and removed by giving the
string used for creation.

The channel name is expected to be a file descriptor
number, or, if parsing the numeric fails, an input file
name that undergoes minimal Filename transformations (no
meta expansion are performed). For example (this example
requires a modern shell):

$ printf 'echon "hey, "\nread a\nyou\necho $a' |\
s-nail -R#
hey, you
$ LC_ALL=C printf 'echon "hey, "\nread a\necho $a' |\
LC_ALL=C 6<<< 'you' s-nail -R#X'readctl create 6'
hey, you

remove [Only new quoting rules] Removes the named files or
directories. If a name refers to a mailbox, say a Maildir
mailbox, then a mailbox type specific removal will be
performed, deleting the complete mailbox. In interactive
mode the user is asked for confirmation.

rename [Only new quoting rules] Takes the name of an existing
folder and the name for the new folder and renames the
first to the second one. Filename transformations
including shell pathname wildcard pattern expansions
(glob(7)) are performed on both arguments. Both folders
must be of the same type.

Reply, Respond
(Compose mode)(R) Identical to reply except that it
replies to only the sender of each message of the given
list, by using the first message as the template to quote,
for the `Subject:' etc.; setting flipr will exchange this
command with reply.

reply, respond
(Compose mode)(r) Take a message (list) and group-respond
(to each in turn) by addressing the sender and all
recipients, subject to fullnames and alternates
processing. followup-to, followup-to-honour,
reply-to-honour as well as recipients-in-cc influence
response behaviour. quote as well as quote-as-attachment
configure whether responded-to message shall be quoted
etc., content-description-quote-attachment may be used.
Setting flipr will exchange this command with Reply. The
command Lreply offers special support for replying to
mailing lists. For more documentation please refer to On
sending mail, and non-interactive mode.

This may generate the errors ^ERR-DESTADDRREQ if no
receiver has been specified, or was rejected by expandaddr
policy, ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a
necessary character set conversion fails, and ^ERR-INVAL
for other errors. It can also fail with errors of
Specifying messages. Any error stops processing of
further messages.

Resend Like resend, but does not add any header lines. This is
not a way to hide the sender's identity, but useful for
sending a message again to the same recipients.

resend Takes a list of messages and a name, and sends each
message to the given addressee, which is subject to
fullnames. `Resent-From:' and related header fields are
prepended to the new copy of the message. Saving in
record is only performed if record-resent is set. [v15
behaviour may differ](Compose mode) is not entered, the
only supported hooks are on-resend-enter and
on-resend-cleanup.

This may generate the errors ^ERR-DESTADDRREQ if no
receiver has been specified, or was rejected by expandaddr
policy, ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a
necessary character set conversion fails, and ^ERR-INVAL
for other errors. It can also fail with errors of
Specifying messages. Any error stops processing of
further messages.

retain (ret) Superseded by the multiplexer headerpick.

return Only available inside of a defined macro or an account,
this command returns control of execution to the outer
scope. The two optional parameters are positive decimal
numbers and default to 0: the first specifies the 32-bit
return value (stored in ? [v15 behaviour may differ] and
later extended to 64-bit), the second the 32-bit error
number (stored in !). As documented for ? a non-0 exit
status may cause the program to exit.

Save (S) Similar to save, but saves the messages in a file
named after the local part of the sender of the first
message instead of taking a filename argument; outfolder
is inspected to decide on the actual storage location.

save (s) Takes a message list and a filename and appends each
message in turn to the end of the file. Filename
transformations including shell pathname wildcard pattern
expansions (glob(7)) is performed on the filename. If no
filename is given, the secondary mailbox MBOX is used.
The filename in quotes, followed by the generated
character count is echoed on the user's terminal. If
editing a primary system mailbox the messages are marked
for deletion. To filter the saved header fields to the
desired subset use the `save' slot of the white- and
blacklisting command headerpick. Also see Copy.

savediscard [Obsolete] Superseded by the multiplexer headerpick.

saveignore [Obsolete] Superseded by the multiplexer headerpick.

saveretain [Obsolete] Superseded by the multiplexer headerpick.

search Takes a message specification (list) and displays a header
summary of all matching messages, as via headers. This
command is an alias of from. Also see Specifying
messages.

seen Takes a message list and marks all messages as having been
read.

set, unset (se, [Only new quoting rules] uns) The latter command will
delete all given global variables, or only block-scope
local ones if the local command modifier has been used.
The former, when used without arguments, will show all
currently known variables, being more verbose if either of
debug or verbose is set. Remarks: this list mode will not
automatically link-in (known) ENVIRONMENT variables, this
only happens for explicit addressing, examples are
varshow, using a variable in an if condition or a string
passed to echo, explicit setting, as well as some program-
internal use cases (look-ups).

Otherwise the given variables (and arguments) are set or
adjusted. Arguments are of the form `name=value' (no
space before or after `='), or plain `name' if there is no
value, i.e., a boolean variable. If a name begins with
`no', as in `set nosave', the effect is the same as
invoking the unset command with the remaining part of the
variable (`unset save'). [v15 behaviour may differ] In
conjunction with the wysh (or local) command prefix(es)
Shell-style argument quoting can be used to quote
arguments as necessary. [v15 behaviour may differ]
Otherwise quotation marks may be placed around any part of
the assignment statement to quote blanks or tabs.

When operating in global scope any `name' that is known to
map to an environment variable will automatically cause
updates in the program environment (unsetting a variable
in the environment requires corresponding system support)
-- use the command environ for further environmental
control. If the command modifier local has been used to
enforce local scoping then the given user variables will
be garbage collected when the local scope is left; for
INTERNAL VARIABLES, however, local behaves the same as if
localopts would have been set (temporarily), which means
that changes are inherited by deeper scopes. Also see
varshow and the sections INTERNAL VARIABLES and
ENVIRONMENT.

? wysh set indentprefix=' -> '
? wysh set atab=$'' aspace=' ' zero=0

shcodec Apply shell quoting rules to the given raw-data arguments.
Supports vput (see Command modifiers). The first argument
specifies the operation: [+]e[ncode] or d[ecode] cause
shell quoting to be applied to the remains of the line,
and expanded away thereof, respectively. If the former is
prefixed with a plus-sign, the quoted result will not be
roundtrip enabled, and thus can be decoded only in the
very same environment that was used to perform the encode;
also see mle-quote-rndtrip. If the coding operation fails
the error number ! is set to ^ERR-CANCELED, and the
unmodified input is used as the result; the error number
may change again due to output or result storage errors.

shell [Only new quoting rules] (sh) Invokes an interactive
version of the shell, and returns its exit status.

shortcut, unshortcut
[Only new quoting rules] Manage the file- or pathname
shortcuts as documented for folder. The latter command
deletes all shortcuts given as arguments, or all at once
when given the asterisk `*'. The former shows the list of
all currently defined shortcuts if used without arguments,
the target of the given with a single argument. Otherwise
arguments are treated as pairs of shortcuts and their
desired expansion, creating new or updating already
existing ones.

shift [Only new quoting rules] Shift the positional parameter
stack (starting at 1) by the given number (which must be a
positive decimal), or 1 if no argument has been given. It
is an error if the value exceeds the number of positional
parameters. If the given number is 0, no action is
performed, successfully. The stack as such can be managed
via vpospar. Note this command will fail in account and
hook macros unless the positional parameter stack has been
explicitly created in the current context via vpospar.

show Like type, but performs neither MIME decoding nor
decryption, so that the raw message text is shown.

size (si) Shows the size in characters of each message of the
given message list.

sleep [Only new quoting rules] Sleep for the specified number of
seconds (and optionally milliseconds), by default
interruptible. If a third argument is given the sleep
will be uninterruptible, otherwise the error number ! will
be set to ^ERR-INTR if the sleep has been interrupted.
The command will fail and the error number will be
^ERR-OVERFLOW if the given duration(s) overflow the time
datatype, and ^ERR-INVAL if the given durations are no
valid integers.

sort, unsort
The latter command disables sorted or threaded mode,
returns to normal message order and, if the header
variable is set, displays a header summary. The former
command shows the current sorting criterion when used
without an argument, but creates a sorted representation
of the current folder otherwise, and changes the next
command and the addressing modes such that they refer to
messages in the sorted order. Message numbers are the
same as in regular mode. If the header variable is set, a
header summary in the new order is also displayed.
Automatic folder sorting can be enabled by setting the
autosort variable, as in `set autosort=thread'. Possible
sorting criterions are:

date Sort the messages by their `Date:' field, that is
by the time they were sent.
from Sort messages by the value of their `From:'
field, that is by the address of the sender. If
the showname variable is set, the sender's real
name (if any) is used.
size Sort the messages by their size.
spam [Option] Sort the message by their spam score, as
has been classified by spamrate.
status Sort the messages by their message status.
subject Sort the messages by their subject.
thread Create a threaded display.
to Sort messages by the value of their `To:' field,
that is by the address of the recipient. If the
showname variable is set, the recipient's real
name (if any) is used.

source [Only new quoting rules] (so) The source command reads
commands from the given file. Filename transformations
will be applied. If the given expanded argument ends with
a vertical bar `|' then the argument will instead be
interpreted as a shell command and S-nail will read the
output generated by it. Dependent on the settings of
posix and errexit, and also dependent on whether the
command modifier ignerr had been used, encountering errors
will stop sourcing of the given input. [v15 behaviour may
differ] Note that source cannot be used from within macros
that execute as folder-hooks or accounts, i.e., it can
only be called from macros that were called.

source_if [Only new quoting rules] The difference to source (beside
not supporting pipe syntax aka shell command input) is
that this command will not generate an error nor warn if
the given file argument cannot be opened successfully.

spamclear [Option] Takes a list of messages and clears their
`is-spam' flag.

spamforget [Option] Takes a list of messages and causes the
spam-interface to forget it has ever used them to train
its Bayesian filter. Unless otherwise noted the `is-spam'
flag of the message is inspected to chose whether a
message shall be forgotten to be "ham" or "spam".

spamham [Option] Takes a list of messages and informs the Bayesian
filter of the spam-interface that they are "ham". This
also clears the `is-spam' flag of the messages in
question.

spamrate [Option] Takes a list of messages and rates them using the
configured spam-interface, without modifying the messages,
but setting their `is-spam' flag as appropriate; because
the spam rating headers are lost the rate will be
forgotten once the mailbox is left. Refer to the manual
section Handling spam for the complete picture of spam
handling in S-nail.

spamset [Option] Takes a list of messages and sets their `is-spam'
flag.

spamspam [Option] Takes a list of messages and informs the Bayesian
filter of the spam-interface that they are "spam". This
also sets the `is-spam' flag of the messages in question.

thread [Obsolete] The same as `sort thread' (consider using a
`commandalias' as necessary).

tls [Only new quoting rules] TLS information and management
command multiplexer to aid in Encrypted network
communication, mostly available only if the term
`,+sockets,' is included in features. Commands support
vput if so documented (see Command modifiers). The result
that is shown in case of errors is always the empty
string, errors can be identified via the error number !.
For example, string length overflows are caught and set !
to ^ERR-OVERFLOW. The TLS configuration is honoured,
especially tls-verify.

? vput tls result fingerprint pop3s://ex.am.ple
? echo $?/$!/$^ERRNAME: $result

certchain Show the complete verified peer certificate
chain. Includes informational fields in
conjunction with verbose.

certificate Show only the peer certificate, without any
signers. Includes informational fields in
conjunction with verbose.

fingerprint Show the tls-fingerprint-digested
fingerprint of the certificate of the given
HOST (`server:port', where the port
defaults to the HTTPS port, 443).
tls-fingerprint is actively ignored for the
runtime of this command.

Top Like top but always uses the headerpick `type' slot for
white- and blacklisting header fields.

top (to) Takes a message list and types out the first toplines
lines of each message on the user's terminal. Unless a
special selection has been established for the `top' slot
of the headerpick command, the only header fields that are
displayed are `From:', `To:', `Cc:', and `Subject:'. Top
will always use the `type' headerpick selection instead.
It is possible to apply compression to what is displayed
by setting topsqueeze. Messages are decrypted and
converted to the terminal character set if necessary.

touch (tou) Takes a message list and marks the messages for
saving in the secondary mailbox MBOX. S-nail deviates
from the POSIX standard with this command, as a following
next command will display the following message instead of
the current one.

Type (T) Like type but also displays header fields which would
not pass the headerpick selection, and all visualizable
parts of MIME `multipart/alternative' messages.

type (t) Takes a message list and types out each message on the
user's terminal. The display of message headers is
selectable via headerpick. For MIME multipart messages,
all parts with a content type of `text', all parts which
have a registered MIME type handler (see HTML mail and
MIME attachments) which produces plain text output, and
all `message' parts are shown, others are hidden except
for their headers. Messages are decrypted and converted
to the terminal character set if necessary. The command
mimeview can be used to display parts which are not
displayable as plain text.

unaccount See account.

unalias (una) See alias.

unanswered See answered.

unbind See bind.

uncollapse See collapse.

uncolour See colour.

undefine See define.

undelete See delete.

undraft See draft.

unflag See flag.

unfwdignore [Obsolete] Superseded by the multiplexer headerpick.

unfwdretain [Obsolete] Superseded by the multiplexer headerpick.

unignore Superseded by the multiplexer headerpick.

unmimetype See mimetype.

unmlist See mlist.

unmlsubscribe
See mlsubscribe.

Unread Same as unread.

unread Takes a message list and marks each message as not having
been read.

unretain Superseded by the multiplexer headerpick.

unsaveignore
[Obsolete] Superseded by the multiplexer headerpick.

unsaveretain
[Obsolete] Superseded by the multiplexer headerpick.

unset [Only new quoting rules] (uns) See set.

unshortcut See shortcut.

unsort See short.

unthread [Obsolete] Same as unsort.

urlcodec Perform URL percent codec operations on the raw-data
argument, rather according to RFC 3986. The first
argument specifies the operation: e[ncode] or d[ecode]
perform plain URL percent en- and decoding, respectively.
p[ath]enc[ode] and p[ath]dec[ode] perform a slightly
modified operation which should be better for pathnames:
it does not allow a tilde `~', and will neither accept
hyphen-minus `-' nor dot `'. as an initial character.
The remains of the line form the URL data which is to be
converted. This is a character set agnostic operation,
and it may thus decode bytes which are invalid in the
current ttycharset.

Supports vput (see Command modifiers), and manages the
error number !. If the coding operation fails the error
number ! is set to ^ERR-CANCELED, and the unmodified input
is used as the result; the error number may change again
due to output or result storage errors. [v15 behaviour
may differ] This command does not know about URLs beside
what is documented. (vexpr offers a makeprint subcommand,
shall the URL be displayed.)

varshow [Only new quoting rules] This command produces the same
output as the listing mode of set, including verboseity
adjustments, but only for the given variables.

verify [Option] Takes a message list and verifies each message.
If a message is not a S/MIME signed message, verification
will fail for it. The verification process checks if the
message was signed using a valid certificate, if the
message sender's email address matches one of those
contained within the certificate, and if the message
content has been altered.

version Shows the version and features of S-nail, optionally in a
more verbose form which also includes the build and
running system environment. This command supports vput
(see Command modifiers).

vexpr [Only new quoting rules] A multiplexer command which
offers signed 64-bit numeric calculations, as well as
other, mostly string-based operations. C-style byte
string operations are available via csop. The first
argument defines the number, type, and meaning of the
remaining arguments. An empty number argument is treated
as 0. Supports vput (see Command modifiers). The result
shown in case of errors is `-1' for usage errors and
numeric operations, the empty string otherwise; "soft"
errors, like when a search operation failed, will also set
the ! error number to ^ERR-NODATA. Except when otherwise
noted numeric arguments are parsed as signed 64-bit
numbers, and errors will be reported in the error number !
as the numeric error ^ERR-RANGE.

Numeric operations work on one or two signed 64-bit
integers. Numbers prefixed with `0x' or `0X' are
interpreted as hexadecimal (base 16) numbers, whereas `0'
indicates octal (base 8), and `0b' as well as `0B' denote
binary (base 2) numbers. It is possible to use any base
in between 2 and 36, inclusive, with the `BASE#number'
notation, where the base is given as an unsigned decimal
number, so `16#AFFE' is a different way of specifying a
hexadecimal number. Unsigned interpretation of a number
can be enforced by prefixing an `u' (case-insensitively),
as in `u-110'; this is not necessary for power-of-two
bases (2, 4, 8, 16 and 32), which will be interpreted as
unsigned by default, but it still makes a difference
regarding overflow detection and overflow constant. It is
possible to enforce signed interpretation by (instead)
prefixing a `s' (case-insensitively). The number sign
notation uses a permissive parse mode and as such supports
complicated conditions out of the box:

? wysh set ifs=:;read i;unset ifs;echo $i;vexpr pb 2 10#$i
-009
< -009>
0b1001

One integer is expected by assignment (equals sign `='),
which does nothing but parsing the argument, thus
detecting validity and possible overflow conditions, unary
not (tilde `~'), which creates the bitwise complement, and
unary plus and minus. Two integers are used by addition
(plus sign `+'), subtraction (hyphen-minus `-'),
multiplication (asterisk `*'), division (solidus `/') and
modulo (percent sign `%'), as well as for the bitwise
operators logical or (vertical bar `|', to be quoted) ,
bitwise and (ampersand `&', to be quoted) , bitwise xor
(circumflex `^'), the bitwise signed left- and right
shifts (`<<', `>>'), as well as for the unsigned right
shift `>>>'.

Another numeric operation is pbase, which takes a number
base in between 2 and 36, inclusive, and will act on the
second number given just the same as what equals sign `='
does, but the number result will be formatted in the base
given, as a signed 64-bit number unless unsigned
interpretation of the input number had been forced (with
an u prefix).

Numeric operations support a saturated mode via the
question mark `?' modifier suffix; the keyword `saturated'
is optional, `+?', `+?satu', and `+?saturated' are
therefore identical. In saturated mode overflow errors
and division and modulo by zero are no longer reported via
the exit status, but the result will linger at the minimum
or maximum possible value, instead of overflowing (or
trapping). This is true also for the argument parse step.
For the bitwise shifts, the saturated maximum is 63. Any
caught overflow will be reported via the error number ! as
^ERR-OVERFLOW.

? vput vexpr res -? +1 -9223372036854775808
? echo $?/$!/$^ERRNAME:$res
0/75/OVERFLOW:-9223372036854775808

Character set agnostic string functions have no notion of
locale settings and character sets.

date-utc Outputs the current date and time in UTC
(Coordinated Universal Time) with values
named such that `vput vexpr x date-utc;
eval wysh set $x' creates accessible
variables.

date-stamp-utc Outputs a RFC 3339 internet date/time
format of UTC.

epoch The seconds and nanoseconds since the Unix
epoch (1970-01-01T00:00:00) named
`epoch_sec' and `epoch_nsec' such that
`vput vexpr x epoch; eval wysh set $x'
creates accessible variables.

file-expand Performs the usual Filename transformations
on its argument.

file-stat, file-lstat Perform the usual Filename
transformations on the argument, then call
stat(2) and lstat(2), respectively, and
output values such that `vput vexpr x
file-stat FILE; eval wysh set $x' creates
accessible variables. The variable
`st_type' uses solidus `/' to denote
directories, commercial at `@' for links,
number sign `#' for block devices, percent
sign `%' for for character devices,
vertical bar `|' for FIFOs, equal sign `='
for sockets, and the period `.' for the
rest.

random Generates a random string of the given
length, or of PATH_MAX bytes (a constant
from /usr/include) if the value 0 is given;
the random string will be base64url encoded
according to RFC 4648, and thus be usable
as a (portable) filename.

String operations work, sufficient support provided,
according to the active user's locale encoding and
character set (see Character sets). Where the question
mark `?' modifier suffix is supported, a case-insensitive
operation mode is available; the keyword `case' is
optional, `regex?' and `regex?case' are therefore
identical.

makeprint (One-way) Converts the argument to something
safely printable on the terminal.

regex [Option] A string operation that will try to
match the first argument with the regular
expression given as the second argument.
`?' modifier suffix is supported. If the
optional third argument has been given then
instead of showing the match offset a
replacement operation is performed: the
third argument is treated as if specified
within dollar-single-quote (see Shell-style
argument quoting), and any occurrence of a
positional parameter, for example 0, 1 etc.
is replaced with the according match group
of the regular expression:

? vput vexpr res regex bananarama \
(.*)NanA(.*) '\${1}au\$2'
? echo $?/$!/$^ERRNAME:$res:
1/61/NODATA::
? vput vexpr res regex?case bananarama \
(.*)NanA(.*) '\${1}uauf\$2'
? echo $?/$!/$^ERRNAME:$res:
0/0/NONE:bauauframa:

vpospar [Only new quoting rules] Manage the positional parameter
stack (see 1, #, *, @ as well as shift). If the first
argument is `clear', then the positional parameter stack
of the current context, or the global one, if there is
none, is cleared. If it is `set', then the remaining
arguments will be used to (re)create the stack, if the
parameter stack size limit is excessed an ^ERR-OVERFLOW
error will occur.

If the first argument is `quote', a round-trip capable
representation of the stack contents is created, with each
quoted parameter separated from each other with the first
character of ifs, and followed by the first character of
if-ws, if that is not empty and not identical to the
first. If that results in no separation at all a space
character is used. This mode supports vput (see Command
modifiers). I.e., the subcommands `set' and `quote' can
be used (in conjunction with eval) to (re)create an
argument stack from and to a single variable losslessly.

? vpospar set hey, "'you ", world!
? echo $#: <${1}><${2}><${3}>
? vput vpospar x quote
? vpospar clear
? echo $#: <${1}><${2}><${3}>
? eval vpospar set ${x}
? echo $#: <${1}><${2}><${3}>

visual (v) Takes a message list and invokes the VISUAL display
editor on each message. Modified contents are discarded
unless the writebackedited variable is set, and are not
used unless the mailbox can be written to and the editor
returns a successful exit status. edit can be used
instead for a less display oriented editor.

write (w) For conventional messages the body without all headers
is written. The original message is never marked for
deletion in the originating mail folder. The output is
decrypted and converted to its native format as necessary.
If the output file exists, the text is appended. If a
message is in MIME multipart format its first part is
written to the specified file as for conventional
messages, handling of the remains depends on the execution
mode. No special handling of compressed files is
performed.

In interactive mode the user is consecutively asked for
the filenames of the processed parts. For convenience
saving of each part may be skipped by giving an empty
value, the same result as writing it to /dev/null. Shell
piping the part content by specifying a leading vertical
bar `|' character for the filename is supported. Other
user input undergoes the usual Filename transformations,
including shell pathname wildcard pattern expansions
(glob(7)) and shell variable expansion for the message as
such, not the individual parts, and contents of the
destination file are overwritten if the file previously
existed. Character set conversion to ttycharset is
performed when saving text data.

[v15 behaviour may differ] In non-interactive mode any
part which does not specify a filename is ignored, and
suspicious parts of filenames of the remaining parts are
URL percent encoded (as via urlcodec) to prevent injection
of malicious character sequences, resulting in a filename
that will be written into the current directory. Existing
files will not be overwritten, instead the part number or
a dot are appended after a number sign `#' to the name
until file creation succeeds (or fails due to other
reasons).

xcall [Only new quoting rules] The sole difference to call is
that the new macro is executed in place of the current
one, which will not regain control: all resources of the
current macro will be released first. This implies that
any setting covered by localopts will be forgotten and
covered variables will become cleaned up. If this command
is not used from within a called macro it will silently be
(a more expensive variant of) call.

xit (x) A synonym for exit.

z [Only new quoting rules] S-nail presents message headers
in screenfuls as described under the headers command.
Without arguments this command scrolls to the next window
of messages, likewise if the argument is `+'. An argument
of `-' scrolls to the last, `^' scrolls to the first, and
`$' to the last screen of messages. A number argument
prefixed by `+' or `-' indicates that the window is
calculated in relation to the current position, and a
number without a prefix specifies an absolute position.

Z [Only new quoting rules] Similar to z, but scrolls to the
next or previous window that contains at least one `new'
or flagged message.

COMMAND ESCAPES

Command escapes are available in Compose mode during interactive usage,
when explicitly requested via -~, and in batch mode (-#). They perform
special functions, like editing headers of the message being composed,
calling normal COMMANDS, yielding a shell, etc. Command escapes are
only recognized at the beginning of lines, and consist of an escape
followed by a command character. The default escape character is the
tilde `~'.

Unless otherwise documented command escapes ensure proper updates of
the error number ! and the exit status ?. The variable errexit
controls whether a failed operation errors out message compose mode and
causes program exit. Escapes may be prefixed by none to multiple
single character command modifiers, interspersed whitespace is ignored:

+o An effect equivalent to the command modifier ignerr can be achieved
with hyphen-minus `-', overriding errexit.

+o The modifier dollar `$' evaluates the remains of the line; also see
Shell-style argument quoting. [v15 behaviour may differ] For now
the entire input line is evaluated as a whole; to avoid that
control operators like semicolon ; are interpreted unintentionally,
they must be quoted.

Addition of the command line to the [Option]al history can be prevented
by placing whitespace directly after escape. The [Option]al key
bindings support a compose mode specific context. The following
command escapes are supported:

~~ string Insert the string of text in the message prefaced by a
single `~'. (If the escape character has been changed,
that character must be doubled instead.)

~! command Execute the indicated shell command which follows,
replacing unescaped exclamation marks with the previously
executed command if the internal variable bang is set,
then return to the message.

~. End compose mode and send the message. The hooks
on-compose-splice-shell and on-compose-splice, in order,
will be called when set, after which, in interactive mode
askatend (leading to askcc, askbcc) and askattach will be
checked as well as asksend, after which a set
on-compose-leave hook will be called, autocc and autobcc
will be joined in if set, finally a given
message-inject-tail will be incorporated, after which the
compose mode is left.

~: S-nail-command or ~_ S-nail-command
Can be used to execute COMMANDS (which are allowed in
compose mode).

~< filename Identical to ~r.

~<! command command is executed using the shell. Its standard output
is inserted into the message.

~? [Option] Write a summary of command escapes.

~@ [filename...]
Append or edit the list of attachments. Does not manage
the error number ! and the exit status ? (please use ~^ if
error handling is necessary). The append mode expects a
list of filename arguments as shell tokens (see Shell-
style argument quoting; token-separating commas are
ignored, too), to be interpreted as documented for the
command line option -a, with the message number exception
as below.

Without filename arguments the attachment list is edited,
entry by entry; if a filename is left empty, that
attachment is deleted from the list; once the end of the
list is reached either new attachments may be entered or
the session can be quit by committing an empty "new"
attachment. In non-interactive mode or in batch mode (-#)
the list of attachments is effectively not edited but
instead recreated; again, an empty input ends list
creation.

For all modes, if a given filename solely consists of the
number sign `#' followed by either a valid message number
of the currently active mailbox, or by a period `.',
referring to the current message of the active mailbox,
the so-called "dot", then the given message is attached as
a `message/rfc822' MIME message part. The number sign
must be quoted to avoid misinterpretation as a shell
comment character.

~| command Pipe the message text through the specified filter
command. If the command gives no output or terminates
abnormally, retain the original text of the message. The
command fmt(1) is often used as a rejustifying filter.

If the first character of the command is a vertical bar,
then the entire message including header fields is subject
to the filter command, so `~|| echo Fcc: /tmp/test; cat'
will prepend a file-carbon-copy message header. Also see
~e, ~v.

~^ cmd [subcmd [arg3 [arg4]]]
Inspect and modify the message using the semantics of
digmsg, therefore arguments are evaluated according to
Shell-style argument quoting. Error number ! and exit
status ? are not managed: errors are handled via the
protocol, and hard errors like I/O failures cannot be
handled.

The protocol consists of command lines followed by (a)
response line(s). The first field of the response line
represents a status code which specifies whether a command
was successful or not, whether result data is to be
expected, and if, the format of the result data. Response
data will be shell quoted as necessary for consumption by
readsh, or eval and vpospar, to name a few. Error status
code lines may optionally contain additional context:

`210' Status ok; the remains of the line are the
result.
`211' Status ok; the rest of the line is optionally
used for more status. What follows are lines
of result addresses, terminated by an empty
line. All the input, including the empty
line, must be consumed before further commands
can be issued. Address lines consist of two
token, first the plain network address, e.g.,
`bob@exam.ple', followed by the (quoted) full
address as known: `'(Lovely) Bob
<bob@exam.ple>''. Non-network addresses use
the first field to indicate the type (hyphen-
minus `-' for files, vertical bar `|' for
pipes, and number sign `#' for names which
will undergo alias processing) instead, the
actual value will be in the second field.
`212' Status ok; the rest of the line is optionally
used for more status. What follows are lines
of furtherly unspecified (quoted) string
content, terminated by an empty line. All the
input, including the empty line, must be
consumed before further commands can be
issued.
`500' Syntax error; invalid command.
`501' Syntax error or otherwise invalid parameters
or arguments.
`505' Error: an argument fails verification. For
example an invalid address has been specified
(also see expandaddr), or an attempt was made
to modify anything in S-nail's own namespace,
or a modifying subcommand has been used on a
read-only message.
`506' Error: an otherwise valid argument is rendered
invalid due to context. For example, a second
address is added to a header which may consist
of a single address only.

If a command indicates failure then the message will have
remained unmodified. Most commands can fail with `500' if
required arguments are missing, or excessive arguments
have been given (false command usage). ([v15 behaviour
may differ] The latter does not yet occur regularly,
because as stated in Shell-style argument quoting our
argument parser is not yet smart enough to work on
subcommand base; for example one might get excess argument
error for a three argument subcommand that receives four
arguments, but not for a four argument subcommand which
receives six arguments: here excess will be joined.) The
following (case-insensitive) commands are supported:

attachment This command allows listing, removal and
addition of message attachments. The
second argument specifies the subcommand
to apply, one of:

attribute This uses the same search
mechanism as described for
remove and prints any known
attributes of the first
found attachment via `212'
upon success or `501' if no
such attachment can be
found. The attributes are
written as lines with a
keyword and a value token.

attribute-at This uses the same search
mechanism as described for
remove-at and is otherwise
identical to attribute.

attribute-set This uses the same search
mechanism as described for
remove, and will set the
attribute given as the
fourth to the value given
as the fifth token
argument. If the value is
an empty token, then the
given attribute is removed,
or reset to a default value
if existence of the
attribute is crucial.

It returns via `210' upon
success, with the index of
the found attachment
following, `505' for
message attachments or if
the given keyword is
invalid, and `501' if no
such attachment can be
found. The following
keywords may be used (case-
insensitively):

`filename' Sets the
filename
of the
MIME part,
i.e., the
name that
is used
for
display
and when
(suggesting
a name
for)
saving
(purposes).
`content-description' Associate
some
descriptive
information
to the
attachment's
content,
used in
favour of
the plain
filename
by some
MUAs.
`content-id' May be
used for
uniquely
identifying
MIME
entities
in several
contexts;
this
expects a
special
reference
address
format as
defined in
RFC 2045
and
generates
a `505'
upon
address
content
verification
failure.
`content-type' Defines
the media
type/subtype
of the
part,
which is
managed
automatically,
but can be
overwritten.
`content-disposition' Automatically
set to the
string
`attachment'.

attribute-set-at This uses the same search
mechanism as described for
remove-at and is otherwise
identical to attribute-set.

insert Adds the attachment given
as the third argument,
specified exactly as
documented for the command
line option -a, and
supporting the message
number extension as
documented for ~@. This
reports `210' upon success,
with the index of the new
attachment following, `505'
if the given file cannot be
opened, `506' if an on-the-
fly performed character set
conversion fails, otherwise
`501' is reported; this is
also reported if character
set conversion is requested
but not available.

list List all attachments via
`212', or report `501' if
no attachments exist. This
command is the default
command of attachment if no
second argument has been
given.

remove This will remove the
attachment given as the
third argument, and report
`210' upon success or `501'
if no such attachment can
be found. If there exists
any path component in the
given argument, then an
exact match of the path
which has been used to
create the attachment is
used directly, but if only
the basename of that path
matches then all
attachments are traversed
to find an exact match
first, and the removal
occurs afterwards; if
multiple basenames match, a
`506' error occurs.
Message attachments are
treated as absolute
pathnames.

If no path component exists
in the given argument, then
all attachments will be
searched for `filename='
parameter matches as well
as for matches of the
basename of the path which
has been used when the
attachment has been
created; multiple matches
result in a `506'.

remove-at This will interpret the
third argument as a number
and remove the attachment
at that list position
(counting from one!),
reporting `210' upon
success or `505' if the
argument is not a number or
`501' if no such attachment
exists.

header This command allows listing, inspection,
and editing of message headers. Header
name case is not normalized, so that case-
insensitive comparison should be used when
matching names. The second argument
specifies the subcommand to apply, one of:

insert Create a new or an
additional instance of the
header given in the third
argument, with the header
body content as given in
the fourth token. It may
return `501' if the third
argument specifies a free-
form header field name that
is invalid, or if body
content extraction fails to
succeed, `505' if any
extracted address does not
pass syntax and/or security
checks or on S-nail
namespace violations, and
`506' to indicate
prevention of excessing a
single-instance header --
note that `Subject:' can be
appended to (a space
separator will be added
automatically first).
`To:', `Cc:' and `Bcc:'
support the `?single'
modifier to enforce
treatment as a single
addressee, for example
`header insert To?single:
'exa, <m@ple>''; the word
`single' is optional.

`210' is returned upon
success, followed by the
name of the header and the
list position of the newly
inserted instance. The
list position is always 1
for single-instance header
fields. All free-form
header fields are managed
in a single list; also see
customhdr.

list Without a third argument a
list of all yet existing
headers is given via `210';
this command is the default
command of header if no
second argument has been
given. A third argument
restricts output to the
given header only, which
may fail with `501' if no
such field is defined.

remove This will remove all
instances of the header
given as the third
argument, reporting `210'
upon success, `501' if no
such header can be found,
and `505' on S-nail
namespace violations.

remove-at This will remove from the
header given as the third
argument the instance at
the list position (counting
from one!) given with the
fourth argument, reporting
`210' upon success or `505'
if the list position
argument is not a number or
on S-nail namespace
violations, and `501' if no
such header instance
exists.

show Shows the content of the
header given as the third
argument. Dependent on the
header type this may
respond with `211' or
`212'; any failure results
in `501'.

In compose-mode read-only access to
optional pseudo headers in the S-nail
private namespace is available:

`Mailx-Command:'
The name of the command that
generates the message, one of
`forward', `Lreply', `mail',
`Reply', `reply', `resend'.
This pseudo header always
exists (in compose-mode).
`Mailx-Raw-To:'
`Mailx-Raw-Cc:'
`Mailx-Raw-Bcc:'
Represent the frozen initial
state of these headers before
any transformation (alias,
alternates, recipients-in-cc
etc.) took place.
`Mailx-Orig-Sender:'
`Mailx-Orig-From:'
`Mailx-Orig-To:'
`Mailx-Orig-Cc:'
`Mailx-Orig-Bcc:'
The values of said headers of
the original message which
has been addressed by any of
reply, forward, resend. The
sender field is special as it
is filled in with the sole
sender according to RFC 5322
rules, it may thus be equal
to the from field.

help, ? Show an abstract of the above commands via
`211'.

version This command will print the protocol
version via `210'.

~A The same as `~i Sign'.

~a The same as `~i sign'.

~b name ... Add the given names to the list of blind carbon copy
recipients.

~c name ... Add the given names to the list of carbon copy recipients.

~d Read the file specified by the DEAD variable into the
message.

~e Invoke the text EDITOR on the message collected so far,
then return to compose mode. ~v can be used for a more
display oriented editor, and ~|| offers a pipe-based
editing approach.

~F messages Read the named messages into the message being sent,
including all message headers and MIME parts, and
honouring forward-add-cc as well as forward-inject-head
and forward-inject-tail. If no messages are specified,
read in the current message, the "dot".

~f messages Read the named messages into the message being sent. If
no messages are specified, read in the current message,
the "dot". Strips down the list of header fields
according to the `forward' (with posix: `type') white- and
blacklist selection of headerpick, and honours
forward-add-cc as well as forward-inject-head and
forward-inject-tail. For MIME multipart messages, only
the first displayable part is included.

~H In interactive mode, edit the message header fields
`From:', `Reply-To:' and `Sender:' by typing each one in
turn and allowing the user to edit the field. The default
values for these fields originate from the from, reply-to
and sender variables. In non-interactive mode this sets
^ERR-NOTTY.

~h In interactive mode, edit the message header fields `To:',
`Cc:', `Bcc:' and `Subject:' by typing each one in turn
and allowing the user to edit the field. In non-
interactive mode this sets ^ERR-NOTTY.

~I variable Insert the value of the specified variable into the
message. The message remains unaltered if the variable is
unset or empty. Any embedded character sequences `\t'
horizontal tabulator and `\n' line feed are expanded in
posix mode; otherwise the expansion should occur at set
time ([v15 behaviour may differ] by using the command
modifier wysh).

~i variable Like ~I, but appends a newline character.

~M messages Read the named messages into the message being sent,
indented by indentprefix. If no messages are specified,
read the current message, the "dot". Honours
forward-add-cc as well as forward-inject-head and
forward-inject-tail.

~m messages Read the named messages into the message being sent,
indented by indentprefix. If no messages are specified,
read the current message, the "dot". Strips down the list
of header fields according to the `type' white- and
blacklist selection of headerpick. Honours forward-add-cc
as well as forward-inject-head and forward-inject-tail.
For MIME multipart messages, only the first displayable
part is included.

~p Display the message collected so far, prefaced by the
message header fields and followed by the attachment list,
if any.

~Q Read in the given / current message(s) using the algorithm
of quote (except that is implicitly assumed, even if not
set), honouring quote-add-cc.

~q Abort the message being sent, copying it to the file
specified by the DEAD variable if save is set.

~R filename Identical to ~r, but indent each line that has been read
by indentprefix.

~r filename [HERE-delimiter]
Read the named file, object to Filename transformations
excluding shell globs and variable expansions, into the
message; if filename is the hyphen-minus `-' then standard
input is used (for pasting, for example). Only in this
latter mode HERE-delimiter may be given: if it is data
will be read in until the given HERE-delimiter is seen on
a line by itself, and encountering EOF is an error; the
HERE-delimiter is a required argument in non-interactive
mode; if it is single-quote quoted then the pasted content
will not be expanded, [v15 behaviour may differ] otherwise
a future version of S-nail may perform shell-style
expansion on the content.

~s string Cause the named string to become the current subject
field. Newline (NL) and carriage-return (CR) bytes are
invalid and will be normalized to space (SP) characters.

~t name ... Add the given name(s) to the direct recipient list.

~U messages Read in the given / current message(s) excluding all
headers, indented by indentprefix. Honours forward-add-cc
as well as forward-inject-head and forward-inject-tail.

~u messages Read in the given / current message(s), excluding all
headers. Honours forward-add-cc as well as
forward-inject-head and forward-inject-tail.

~v Invoke the VISUAL editor on the message collected so far,
then return to compose mode. ~e can be used for a less
display oriented editor, and ~|| offers a pipe-based
editing approach.

~w filename Write the message onto the named file, which is object to
the usual Filename transformations. If the file exists,
the message is appended to it.

~x Same as ~q, except that the message is not saved at all.

INTERNAL VARIABLES

Internal S-nail variables are controlled via the set and unset
commands; prefixing a variable name with the string `no' and calling
set has the same effect as using unset: `unset crt' and `set nocrt' do
the same thing. varshow will give more insight on the given
variable(s), and set, when called without arguments, will show a
listing of all variables. Both commands support a more verbose listing
mode. Some well-known variables will also become inherited from the
program ENVIRONMENT implicitly, others can be imported explicitly with
the command environ and henceforth share said properties.

Two different kinds of internal variables exist, and both of which can
also form chains. There are boolean variables, which can only be in
one of the two states "set" and "unset", and value variables with a(n
optional) string value. For the latter proper quoting is necessary
upon assignment time, the introduction of the section COMMANDS
documents the supported quoting rules.

? wysh set one=val\ 1 two="val 2" \
three='val "3"' four=$'val \'4\''; \
varshow one two three four; \
unset one two three four

Dependent upon the actual option string values may become interpreted
as colour names, command specifications, normal text, etc. They may be
treated as numbers, in which case decimal values are expected if so
documented, but otherwise any numeric format and base that is valid and
understood by the vexpr command may be used, too.

There also exists a special kind of string value, the "boolean string",
which must either be a decimal integer (in which case `0' is false and
`1' and any other value is true) or any of the (case-insensitive)
strings `off', `no', `n' and `false' for a false boolean and `on',
`yes', `y' and `true' for a true boolean; a special kind of boolean
string is the "quadoption": it can optionally be prefixed with the
(case-insensitive) term `ask-', as in `ask-yes'; in interactive mode
the user will be prompted, otherwise the actual boolean is used.

Variable chains extend a plain `variable' with `variable-HOST' and
`variable-USER@HOST' variants. Here `HOST' will be converted to all
lowercase when looked up (but not when the variable is set or unset!),
[Option]ally IDNA converted, and indeed means `server:port' if a `port'
had been specified in the contextual Uniform Resource Locator URL, see
On URL syntax and credential lookup. Even though this mechanism is
based on URLs no URL percent encoding may be applied to neither of
`USER' nor `HOST', variable chains need to be specified using raw data;
the mentioned section contains examples. Variables which support
chains are explicitly documented as such, and S-nail treats the base
name of any such variable special, meaning that users should not create
custom names like `variable-xyz' in order to avoid false
classifications and treatment of such variables.

Initial settings

The standard POSIX 2008/Cor 2-2016 mandates the following initial
variable settings: noallnet, noappend, asksub, noaskbcc, noautoprint,
nobang, nocmd, nocrt, nodebug, nodot, escape set to `~', noflipr,
nofolder, header, nohold, noignore, noignoreeof, nokeep, nokeepsave,
nometoo, nooutfolder, nopage, prompt set to `? ', noquiet, norecord,
save, nosendwait, noshowto, noSign, nosign, toplines set to `5'.

However, S-nail has built-in some initial (and some default) settings
which (may) diverge, others may become adjusted by one of the Resource
files. Displaying the former is accomplished via set: `$ s-nail -:/ -v
-Xset -Xx'. In general this implementation sets (and has extended the
meaning of) sendwait, and does not support the noonehop variable - use
command line options or mta-arguments to pass options through to a mta.
The default global resource file sets, among others, the variables
hold, keep and keepsave, establishes a default headerpick selection
etc., and should thus be taken into account.

Variables

? (Read-only) The exit status of the last command, or the
return value of the macro called last. This status has a
meaning in the state machine: in conjunction with errexit
any non-0 exit status will cause a program exit, and in
posix mode any error while loading (any of the) resource
files will have the same effect. ignerr, one of the
Command modifiers, can be used to instruct the state
machine to ignore errors.

! (Read-only) The current error number (errno(3)), which is
set after an error occurred; it is also available via
^ERR, and the error name and documentation string can be
queried via ^ERRNAME and ^ERRDOC. [v15 behaviour may
differ] This machinery is new and the error number is only
really usable if a command explicitly states that it
manages the variable !, for others errno will be used in
case of errors, or ^ERR-INVAL if that is 0: it thus may or
may not reflect the real error. The error number may be
set with the command return.

^ (Read-only) This is a multiplexer variable which performs
dynamic expansion of the requested state or condition, of
which there are:

^ERR, ^ERRDOC, ^ERRNAME
The number, documentation, and name of the
current errno(3), respectively, which is
usually set after an error occurred. The
documentation is an [Option], the name is
used if not available. [v15 behaviour may
differ] This machinery is new and is usually
reliable only if a command explicitly states
that it manages the variable !, which is
effectively identical to ^ERR. Each of those
variables can be suffixed with a hyphen minus
followed by a name or number, in which case
the expansion refers to the given error.
Note this is a direct mapping of (a subset
of) the system error values:

define work {
eval echo \$1: \$^ERR-$1:\
\$^ERRNAME-$1: \$^ERRDOC-$1
vput vexpr i + "$1" 1
if [ $i -lt 16 ]
\xcall work $i
end
}
call work 0

^ERRQUEUE-COUNT, ^ERRQUEUE-EXISTS
The number of messages in the [Option]al
queue of errors, and a string indicating
queue state: empty or (translated) "ERROR".
Always 0 and the empty string, respectively,
unless features includes `,+errors,'.

* (Read-only) Expands all positional parameters (see 1),
separated by the first character of the value of ifs.
[v15 behaviour may differ] The special semantics of the
equally named special parameter of the sh(1) are not yet
supported.

@ (Read-only) Expands all positional parameters (see 1),
separated by a space character. If placed in double
quotation marks, each positional parameter is properly
quoted to expand to a single parameter again.

# (Read-only) Expands to the number of positional
parameters, i.e., the size of the positional parameter
stack in decimal.

0 (Read-only) Inside the scope of a defined and called macro
this expands to the name of the calling macro, or to the
empty string if the macro is running from top-level. For
the [Option]al regular expression search and replace
operator of vexpr this expands to the entire matching
expression. It represents the program name in global
context.

1 (Read-only) Access of the positional parameter stack. All
further parameters can be accessed with this syntax, too,
`2', `3' etc.; positional parameters can be shifted off
the stack by calling shift. The parameter stack contains,
for example, the arguments of a called defined macro, the
matching groups of the [Option]al regular expression
search and replace expression of vexpr, and can be
explicitly created or overwritten with the command
vpospar.

account (Read-only) Is set to the active account.

add-file-recipients
(Boolean) When file or pipe recipients have been
specified, mention them in the corresponding address
fields of the message instead of silently stripping them
from their recipient list. By default such addressees are
not mentioned.

allnet (Boolean) Causes only the local part to be evaluated when
comparing addresses.

append (Boolean) Causes messages saved in the secondary mailbox
MBOX to be appended to the end rather than prepended.
This should always be set.

askatend (Boolean) Causes the prompts for `Cc:' and `Bcc:' lists to
appear after the message has been edited.

askattach (Boolean) If set, S-nail asks an interactive user for
files to attach at the end of each message; An empty line
finalizes the list.

askcc (Boolean) Causes the interactive user to be prompted for
carbon copy recipients (at the end of each message if
askatend or bsdcompat are set).

askbcc (Boolean) Causes the interactive user to be prompted for
blind carbon copy recipients (at the end of each message
if askatend or bsdcompat are set).

asksend (Boolean) Causes the interactive user to be prompted for
confirmation to send the message or reenter compose mode
after having been shown a preliminary envelope summary.

asksign (Boolean)[Option] Causes the interactive user to be
prompted if the message is to be signed at the end of each
message. The smime-sign variable is ignored when this
variable is set.

asksub (Boolean) Causes S-nail to prompt the interactive user for
the subject upon entering compose mode unless a subject
already exists.

attrlist A sequence of characters to display in the `attribute'
column of the headline as shown in the display of headers;
each for one type of messages (see Message states), with
the default being `NUROSPMFAT+-$~' or `NU *HMFAT+-$~' if
the bsdflags variable is set, in the following order:

`N' new.
`U' unread but old.
`R' new but read.
`O' read and old.
`S' saved.
`P' preserved.
`M' mboxed.
`F' flagged.
`A' answered.
`T' draft.
`+' [v15 behaviour may differ] start of a
(collapsed) thread in threaded mode (see
autosort, thread);
`-' [v15 behaviour may differ] an uncollapsed thread
in threaded mode; only used in conjunction with
-L.
`$' classified as spam.
`~' classified as possible spam.

autobcc Specifies a list of recipients to which a blind carbon
copy of each outgoing message will be sent automatically.

autocc Specifies a list of recipients to which a carbon copy of
each outgoing message will be sent automatically.

autocollapse
(Boolean) Causes threads to be collapsed automatically
when .Ql thread Ns ed sort mode is entered (see the
collapse command).

autoprint (Boolean) Enable automatic typeing of a(n existing)
"successive" message after delete and undelete commands:
the message that becomes the new "dot" is shown
automatically, as via dp or dt.

autosort Causes sorted mode (see the sort command) to be entered
automatically with the value of this variable as sorting
method when a folder is opened, for example `set
autosort=thread'.

bang (Boolean) Enables the substitution of all not (reverse-
solidus) escaped exclamation mark `!' characters by the
contents of the last executed command for the ! shell
escape command and ~!, one of the compose mode COMMAND
ESCAPES. If this variable is not set no reverse solidus
stripping is performed.

bind-timeout
[Obsolete] Predecessor of bind-inter-byte-timeout. [v15
behaviour may differ] Setting this automatically sets the
successor.

bind-inter-byte-timeout
[Option] Terminals may generate multi-byte sequences for
special function keys, for example, but these sequences
may not become read as a unit. And multi-byte sequences
can be defined freely via bind. This variable specifies
the timeout in milliseconds that the MLE (see On terminal
control and line editor) waits for more bytes to arrive
unless it considers a sequence "complete". The default is
200, the maximum is about 10 seconds. In the following
example the comments state which sequences are affected by
this timeout:

? bind base abc echo 0 # abc
? bind base ab,c echo 1 # ab
? bind base abc,d echo 2 # abc
? bind base ac,d echo 3 # ac
? bind base a,b,c echo 4
? bind base a,b,c,d echo 5
? bind base a,b,cc,dd echo 6 # cc and dd

bind-inter-key-timeout
[Option] Multi-key bind sequences do not time out by
default. If this variable is set, then the current key
sequence is forcefully terminated once the timeout (in
milliseconds) triggers. The value should be (maybe
significantly) larger than bind-inter-byte-timeout, but
may not excess the maximum, too.

bsdcompat (Boolean) Sets some cosmetical features to traditional BSD
style; has the same affect as setting askatend and all
other variables prefixed with `bsd'; it also changes the
behaviour of emptystart (which does not exist in BSD).

bsdflags (Boolean) Changes the letters shown in the first column of
a header summary to traditional BSD style.

bsdheadline (Boolean) Changes the display of columns in a header
summary to traditional BSD style.

bsdmsgs (Boolean) Changes some informational messages to
traditional BSD style.

bsdorder (Boolean) Causes the `Subject:' field to appear
immediately after the `To:' field in message headers and
with the ~h COMMAND ESCAPES.

build-cc, build-ld, build-os, build-rest
(Read-only) The build environment, including the compiler,
the linker, the operating system S-nail has been build
for, usually taken from uname(1) via `uname -s', and then
lowercased, as well as all the possibly interesting rest
of the configuration and build environment. This
information is also available in the verbose output of the
command version.

charset-7bit
The value that should appear in the `charset=' parameter
of `Content-Type:' MIME header fields when no character
set conversion of the message data was performed. This
defaults to US-ASCII, and the chosen character set should
be US-ASCII compatible.

charset-8bit
[Option] The default 8-bit character set that is used as
an implicit last member of the variable sendcharsets.
This defaults to UTF-8 if character set conversion
capabilities are available, and to ISO-8859-1 otherwise
(unless the operating system environment is known to
always and exclusively support UTF-8 locales), in which
case the only supported character set is ttycharset and
this variable is effectively ignored.

charset-unknown-8bit
[Option] RFC 1428 specifies conditions when internet mail
gateways shall "upgrade" the content of a mail message by
using a character set with the name `unknown-8bit'.
Because of the unclassified nature of this character set
S-nail will not be capable to convert this character set
to any other character set. If this variable is set any
message part which uses the character set `unknown-8bit'
is assumed to really be in the character set given in the
value, otherwise the (final) value of charset-8bit is used
for this purpose.

This variable will also be taken into account if a MIME
type (see The mime.types files) of a MIME message part
that uses the `binary' character set is forcefully treated
as text.

cmd The default value for the pipe command.

colour-disable
(Boolean)[Option] Forcefully disable usage of colours.
Also see the section Coloured display.

colour-pager
(Boolean)[Option] Whether colour shall be used for output
that is paged through PAGER. Note that pagers may need
special command line options, for example less(1) requires
the option -R and lv(1) the option -c in order to support
colours. Often doing manual adjustments is unnecessary
since S-nail may perform adjustments dependent on the
value of the environment variable PAGER (see there for
more).

contact-mail, contact-web
(Read-only) Addresses for contact per email and web,
respectively, for bug reports, suggestions, or anything
else regarding S-nail. The former can be used directly:
`? eval mail $contact-mail'.

content-description-forwarded-message,
content-description-quote-attachment,
content-description-smime-message,
content-description-smime-signature
[Option](partially) Strings which will be placed in
according `Content-Description:' headers if non-empty.
They all have default values, for example `Forwarded
message'.

crt In a(n interactive) terminal session, then if this valued
variable is set it will be used as a threshold to
determine how many lines the given output has to span
before it will be displayed via the configured PAGER;
Usage of the PAGER can be forced by setting this to the
value `0', setting it without a value will deduce the
current height of the terminal screen to compute the
threshold (see LINES, screen and stty(1)). [v15 behaviour
may differ] At the moment this uses the count of lines of
the message in wire format, which, dependent on the
mime-encoding of the message, is unrelated to the number
of display lines. (The software is old and historically
the relation was a given thing.)

customhdr Define a set of custom headers to be injected into newly
composed or forwarded messages. A custom header consists
of the field name followed by a colon `:' and the field
content body. Standard header field names cannot be
overwritten by a custom header, with the exception of
`Comments:' and `Keywords:'. Different to the command
line option -C the variable value is interpreted as a
comma-separated list of custom headers: to include commas
in header bodies they need to become escaped with reverse
solidus `\'. Headers can be managed more freely in
Compose mode via ~^.

? set customhdr='Hdr1: Body1-1\, Body1-2, Hdr2:
Body2'

datefield Controls the appearance of the `%d' date and time format
specification of the headline variable, that is used, for
example, when viewing the summary of headers. If unset,
then the local receiving date is used and displayed
unformatted, otherwise the message sending `Date:'. It is
possible to assign a strftime(3) format string and control
formatting, but embedding newlines via the `%n' format is
not supported, and will result in display errors. The
default is `%Y-%m-%d %H:%M', and also see
datefield-markout-older.

datefield-markout-older
Only used in conjunction with datefield. Can be used to
create a visible distinction of messages dated more than a
day in the future, or older than six months, a concept
comparable to the -l option of the POSIX utility ls(1).
If set to the empty string, then the plain month, day and
year of the `Date:' will be displayed, but a strftime(3)
format string to control formatting can be assigned. The
default is `%Y-%m-%d'.

debug (Boolean) (Almost) Enter a debug-only sandbox mode which
generates many log messages, disables the actual delivery
of messages, and also implies norecord as well as nosave.
Also see verbose.

disposition-notification-send
(Boolean)[Option] Emit a `Disposition-Notification-To:'
header (RFC 3798) with the message. This requires the
from variable to be set.

dot (Boolean) When dot is set, a period `.' on a line by
itself during message input in (interactive or batch -#)
Compose mode will be treated as end-of-message (in
addition to the normal end-of-file condition). This
behaviour is implied in posix mode with a set ignoreeof.

dotlock-disable
(Boolean)[Option] Disable creation of dotlock files for
MBOX databases.

dotlock-ignore-error
[Obsolete](Boolean)[Option] Ignore failures when creating
dotlock files. Please use dotlock-disable instead.

editalong If this variable is set then the editor is started
automatically when a message is composed in interactive
mode. If the value starts with the letter `v' then this
acts as if ~v, otherwise as if ~e (see COMMAND ESCAPES)
had been specified. The editheaders variable is implied
for this automatically spawned editor session.

editheaders (Boolean) When a message is edited while being composed,
its header is included in the editable text.

emptystart (Boolean) When entering interactive mode S-nail normally
writes "No mail for user" and exits immediately if a
mailbox is empty or does not exist. If this variable is
set S-nail starts even with an empty or non-existent
mailbox (the latter behaviour furtherly depends upon
bsdcompat, though).

errexit (Boolean) Let each command with a non-0 exit status,
including every called macro which returns a non-0 status,
cause a program exit unless prefixed by ignerr (see
Command modifiers). This also affects COMMAND ESCAPES,
but which use a different modifier for ignoring the error.
Please refer to the variable ? for more on this topic.

errors-limit
[Option] Maximum number of entries in the errors queue.

escape The first character of this value defines the escape
character for COMMAND ESCAPES in Compose mode. The
default value is the character tilde `~'. If set to the
empty string, command escapes are disabled.

expandaddr If unset only user name and email address recipients are
allowed On sending mail, and non-interactive mode. If set
without value all possible recipient types will be
accepted. A value is parsed as a comma-separated list of
case-insensitive strings, and if that contains `restrict'
behaviour equals the former except when in interactive
mode or if COMMAND ESCAPES were enabled via -~ or -#, in
which case it equals the latter, allowing all address
types. `restrict' really acts like `restrict,-all,+name,
+addr', so care for ordering issues must be taken.

Recipient types can be added and removed with a plus sign
`+' or hyphen-minus `-' prefix, respectively. By default
invalid or disallowed types are filtered out and cause a
warning, hard send errors need to be enforced by including
`fail'. The value `all' covers all types, `fcc'
whitelists `Fcc:' header targets regardless of other
settings, `file' file targets (it includes `fcc'), `pipe'
command pipeline targets, `name' user names still
unexpanded after alias and mta-aliases processing and thus
left for expansion by the mta (invalid for the built-in
SMTP one), and `addr' network addresses. Targets are
interpreted in the given order, so that `restrict,fail,
+file,-all,+addr' will cause hard errors for any non-
network address recipient address unless running
interactively or having been started with the option -~ or
-#; in the latter case(s) any type may be used.

User name receivers addressing valid local users can be
expanded to fully qualified network addresses (also see
hostname) by including `nametoaddr' in the list.
Historically invalid recipients were stripped off without
causing errors, this can be changed by making
`failinvaddr' an entry of the list (it really acts like
`failinvaddr,+addr'). Likewise, `domaincheck' (really
`domaincheck,+addr') compares address domain names against
a whitelist and strips off (`fail' for hard errors)
addressees which fail this test; the domain name
`localhost' and the non-empty value of hostname (the real
hostname otherwise) are always whitelisted,
expandaddr-domaincheck can be set to extend this list.
Finally some address providers (for example -b, -c and all
other command line recipients) will be evaluated as if
specified within dollar-single-quotes (see Shell-style
argument quoting) if the value list contains the string
`shquote'.

expandaddr-domaincheck
Can be set to a comma-separated list of domain names which
should be whitelisted for the evaluation of the
`domaincheck' mode of expandaddr. IDNA encoding is not
automatically performed, addrcodec can be used to prepare
the domain (of an address).

expandargv Unless this variable is set additional mta (Mail-Transfer-
Agent) arguments from the command line, as can be given
after a -- separator, results in a program termination
with failure status. The same can be accomplished by
using the special (case-insensitive) value `fail'. A
lesser strict variant is the otherwise identical
`restrict', which does accept such arguments in
interactive mode, or if tilde commands were enabled
explicitly by using one of the command line options -~ or
-#. The empty value will allow unconditional usage.

features (Read-only) String giving a list of optional features.
Features are preceded with a plus sign `+' if they are
available, with a hyphen-minus `-' otherwise. To ease
substring matching the string starts and ends with a
comma. The output of the command version includes this
information in a more pleasant output.

flipr (Boolean) This setting reverses the meanings of a set of
reply commands, turning the lowercase variants, which by
default address all recipients included in the header of a
message (reply, respond, followup) into the uppercase
variants, which by default address the sender only (Reply,
Respond, Followup) and vice versa.

folder The default path under which mailboxes are to be saved:
filenames that begin with the plus sign `+' will have the
plus sign replaced with the value of this variable if set,
otherwise the plus sign will remain unchanged when doing
Filename transformations; also see folder for more on this
topic, and know about standard imposed implications of
outfolder. The value supports a subset of transformations
itself, and if the non-empty value does not start with a
solidus `/', then the value of HOME will be prefixed
automatically. Once the actual value is evaluated first,
the internal variable folder-resolved will be updated for
caching purposes.

folder-hook-FOLDER, folder-hook
Names a defined macro which will be called whenever a
folder is opened. The macro will also be invoked when new
mail arrives, but message lists for commands executed from
the macro only include newly arrived messages then.
localopts are activated by default in a folder hook,
causing the covered settings to be reverted once the
folder is left again.

The specialized form will override the generic one if
`FOLDER' matches the file that is opened. Unlike other
folder specifications, the fully expanded name of a
folder, without metacharacters, is used to avoid
ambiguities. However, if the mailbox resides under folder
then the usual `+' specification is tried in addition, so
that if folder is "mail" (and thus relative to the user's
home directory) then /home/usr1/mail/sent will be tried as
`folder-hook-/home/usr1/mail/sent' first, but then
followed by `folder-hook-+sent'.

folder-resolved
(Read-only) Set to the fully resolved path of folder once
that evaluation has occurred; rather internal.

followup-to (Boolean) Controls whether a `Mail-Followup-To:' header is
generated when sending messages to known mailing lists.
The user as determined via from (or, if that contains
multiple addresses, sender) will be placed in there if any
list addressee is not a subscribed list. Also see
followup-to-honour and the commands mlist, mlsubscribe,
reply and Lreply.

followup-to-add-cc
(Boolean) Controls whether the user will be added to the
messages' `Cc:' list in addition to placing an entry in
`Mail-Followup-To:' (see followup-to).

followup-to-honour
Controls whether a `Mail-Followup-To:' header is honoured
when group-replying to a message via reply or Lreply.
This is a quadoption; if set without a value it defaults
to "yes", and see followup-to.

forward-add-cc
(Boolean) Whether senders of messages forwarded via ~F,
~f, ~m, ~U or ~u shall be made members of the carbon
copies `Cc:' list.

forward-as-attachment
(Boolean) Original messages are normally sent as inline
text with the forward command, and only the first part of
a multipart message is included. With this setting
enabled messages are sent as unmodified MIME
`message/rfc822' attachments with all of their parts
included.

forward-inject-head, forward-inject-tail
The strings to put before and after the text of a message
with the forward command, respectively. The former
defaults to `-------- Original Message --------\n'.
Special format directives in these strings will be
expanded if possible, and if so configured the output will
be folded according to quote-fold; for more please refer
to quote-inject-head. Injections will not be performed by
forward if the variable forward-as-attachment is set --
the COMMAND ESCAPES ~F, ~f, ~M, ~m, ~U, ~u always inject.

from The address (or a list of addresses) to put into the
`From:' field of the message header, quoting RFC 5322: the
author(s) of the message, that is, the mailbox(es) of the
person(s) or system(s) responsible for the writing of the
message. According to that RFC setting the sender
variable is required if from contains more than one
address. [v15 behaviour may differ] Please expect
automatic management of the from and sender relationship.
Dependent on the context these addresses are handled as if
they were in the list of alternates.

If a file-based MTA is used, then from (or, if that
contains multiple addresses, sender) can nonetheless be
used as the envelope sender address at the MTA protocol
level (the RFC 5321 reverse-path), either via the -r
command line option (without argument; see there for
more), or by setting r-option-implicit.

If the machine's hostname is not valid at the Internet
(for example at a dialup machine), then either this
variable or hostname ([v15-compat] a SMTP-based mta adds
even more fine-tuning capabilities with smtp-hostname)
have to be set: if so the message and MIME part related
unique ID fields `Message-ID:' and `Content-ID:' will be
created (except when disallowed by message-id-disable or
stealthmua).

fullnames (Boolean) Due to historical reasons comments and name
parts of email addresses are removed by default when
sending mail, replying to or forwarding a message. If
this variable is set such stripping is not performed.

fwdheading [Obsolete] Predecessor of forward-inject-head.

header (Boolean) Causes the header summary to be written at
startup and after commands that affect the number of
messages or the order of messages in the current folder.
Unless in posix mode a header summary will also be
displayed on folder changes. The command line option -N
can be used to set noheader.

headline A format string to use for the summary of headers. Format
specifiers in the given string start with a percent sign
`%' and may be followed by an optional decimal number
indicating the field width -- if that is negative, the
field is to be left-aligned. Names and addresses are
subject to modifications according to showname and showto.
Valid format specifiers are:

`%%' A plain percent sign.
`%>' "Dotmark": a space character but for the
current message ("dot"), for which it expands
to `>' (dependent on headline-plain).
`%<' "Dotmark": a space character but for the
current message ("dot"), for which it expands
to `<' (dependent on headline-plain).
`%$' [Option] The spam score of the message, as
has been classified via the command spamrate.
Shows only a replacement character if there
is no spam support.
`%a' Message attribute character (status flag);
the actual content can be adjusted by setting
attrlist.
`%d' The date found in the `Date:' header of the
message when datefield is set (the default),
otherwise the date when the message was
received. Formatting can be controlled by
assigning a strftime(3) format string to
datefield (and datefield-markout-older).
`%e' The indenting level in `thread'ed sort mode.
`%f' The address of the message sender.
`%i' The message thread tree structure. (Note
that this format does not support a field
width, and honours headline-plain.)
`%L' Mailing list status: is the addressee of the
message a known `l' (mlist) or `L'
mlsubscribed mailing list? The letter `P'
announces the presence of a RFC 2369
`List-Post:' header, which makes a message a
valuable target of Lreply.
`%l' The number of lines of the message, if
available.
`%m' Message number.
`%o' The number of octets (bytes) in the message,
if available.
`%S' Message subject (if any) in double quotes.
`%s' Message subject (if any).
`%t' The position in threaded/sorted order.
`%U' The value 0 except in an IMAP mailbox, where
it expands to the UID of the message.

The default is `%>%a%m %-18f %16d %4l/%-5o %i%-s', or
`%>%a%m %20-f %16d %3l/%-5o %i%-S' if bsdcompat is set.
Also see attrlist, headline-plain and headline-bidi.

headline-bidi
Bidirectional text requires special treatment when
displaying headers, because numbers (in dates or for file
sizes etc.) will not affect the current text direction, in
effect resulting in ugly line layouts when arabic or other
right-to-left text is to be displayed. On the other hand
only a minority of terminals is capable to correctly
handle direction changes, so that user interaction is
necessary for acceptable results. Note that extended host
system support is required nonetheless, e.g., detection of
the terminal character set is one precondition; and this
feature only works in an Unicode (i.e., UTF-8) locale.

In general setting this variable will cause S-nail to
encapsulate text fields that may occur when displaying
headline (and some other fields, like dynamic expansions
in prompt) with special Unicode control sequences; it is
possible to fine-tune the terminal support level by
assigning a value: no value (or any value other than `1',
`2' and `3') will make S-nail assume that the terminal is
capable to properly deal with Unicode version 6.3, in
which case text is embedded in a pair of U+2068 (FIRST
STRONG ISOLATE) and U+2069 (POP DIRECTIONAL ISOLATE)
characters. In addition no space on the line is reserved
for these characters.

Weaker support is chosen by using the value `1' (Unicode
6.3, but reserve the room of two spaces for writing the
control sequences onto the line). The values `2' and `3'
select Unicode 1.1 support (U+200E, LEFT-TO-RIGHT MARK);
the latter again reserves room for two spaces in addition.

headline-plain
(Boolean) On Unicode (UTF-8) aware terminals enhanced
graphical symbols are used by default for certain entries
of headline. If this variable is set only basic US-ASCII
symbols will be used.

history-file
[Option] The (expandable) location of a permanent history
file for the MLE line editor (On terminal control and line
editor). Also see history-size.

history-gabby
[Option] Add more entries to the MLE history as is
normally done. A comma-separated list of case-insensitive
strings can be used to fine-tune which gabby entries shall
be allowed. If it contains `errors', erroneous commands
will also be added. `all' adds all optional entries, and
is the fallback chattiness identifier of
on-history-addition.

history-gabby-persist
(Boolean)[Option] The history-gabby entries will not be
saved in persistent storage unless this variable is set.
The knowledge of whether a persistent entry was gabby is
not lost. Also see history-file.

history-size
[Option] Setting this variable imposes a limit on the
number of concurrent history entries. If set to the value
0 then no further history entries will be added, and
loading and incorporation of the history-file upon program
startup can also be suppressed by doing this. Runtime
changes will not be reflected before the history is saved
or loaded (again).

hold (Boolean) This setting controls whether messages are held
in the system inbox, and it is set by default.

hostname Used instead of the value obtained from uname(3) and
getaddrinfo(3) as the hostname when expanding local
addresses, for example in `From:' (also see On sending
mail, and non-interactive mode, for expansion of addresses
that have a valid user-, but no domain name in angle
brackets). If either of from or this variable is set the
message and MIME part related unique ID fields
`Message-ID:' and `Content-ID:' will be created (except
when disallowed by message-id-disable or stealthmua). If
the [Option]al IDNA support is available (see
idna-disable) variable assignment is aborted when a
necessary conversion fails.

Setting it to the empty string will cause the normal
hostname to be used, but nonetheless enables creation of
said ID fields. [v15-compat] in conjunction with the
built-in SMTP mta smtp-hostname also influences the
results: one should produce some test messages with the
desired combination of hostname, and/or from, sender etc.
first.

idna-disable
(Boolean)[Option] Can be used to turn off the automatic
conversion of domain names according to the rules of IDNA
(internationalized domain names for applications). Since
the IDNA code assumes that domain names are specified with
the ttycharset character set, an UTF-8 locale charset is
required to represent all possible international domain
names (before conversion, that is).

ifs The input field separator that is used ([v15 behaviour may
differ] by some functions) to determine where to split
input data.

1. Unsetting is treated as assigning the default
value, ` \t\n'.
2. If set to the empty value, no field splitting
will be performed.
3. If set to a non-empty value, all whitespace
characters are extracted and assigned to the
variable ifs-ws.

a. ifs-ws will be ignored at the beginning and end
of input. Diverging from POSIX shells default
whitespace is removed in addition, which is owed
to the entirely different line content extraction
rules.
b. Each occurrence of a character of ifs will cause
field-splitting, any adjacent ifs-ws characters
will be skipped.

ifs-ws (Read-only) Automatically deduced from the whitespace
characters in ifs.

ignore (Boolean) Ignore interrupt signals from the terminal while
entering messages; instead echo them as `@' characters and
discard the current line.

ignoreeof (Boolean) Ignore end-of-file conditions (`control-D') in
Compose mode on message input and in interactive command
input. If set an interactive command input session can
only be left by explicitly using one of the commands exit
and quit, and message input in compose mode can only be
terminated by entering a period `.' on a line by itself or
by using the ~. COMMAND ESCAPES; Setting this implies the
behaviour that dot describes in posix mode.

inbox If this is set to a non-empty string it will specify the
user's primary system mailbox, overriding MAIL and the
system-dependent default, and (thus) be used to replace
`%' when doing Filename transformations; also see folder
for more on this topic. The value supports a subset of
transformations itself.

indentprefix
String used by the ~m, ~M and ~R COMMAND ESCAPES and by
the quote option for indenting messages, in place of the
POSIX mandated default tabulator character `\t'. Also see
quote-chars.

keep (Boolean) If set, an empty primary system mailbox file is
not removed. Note that, in conjunction with posix mode
any empty file will be removed unless this variable is
set. This may improve the interoperability with other
mail user agents when using a common folder directory, and
prevents malicious users from creating fake mailboxes in a
world-writable spool directory. [v15 behaviour may
differ] Only local regular (MBOX) files are covered,
Maildir and other mailbox types will never be removed,
even if empty.

keep-content-length
(Boolean) When (editing messages and) writing MBOX mailbox
files S-nail can be told to keep the `Content-Length:' and
`Lines:' header fields that some MUAs generate by setting
this variable. Since S-nail does neither use nor update
these non-standardized header fields (which in itself
shows one of their conceptual problems), stripping them
should increase interoperability in between MUAs that work
with with same mailbox files. Note that, if this is not
set but writebackedited, as below, is, a possibly
performed automatic stripping of these header fields
already marks the message as being modified. [v15
behaviour may differ] At some future time S-nail will be
capable to rewrite and apply an mime-encoding to modified
messages, and then those fields will be stripped silently.

keepsave (Boolean) When a message is saved it is usually discarded
from the originating folder when S-nail is quit. This
setting causes all saved message to be retained.

line-editor-cpl-word-breaks
[Option] List of bytes which are used by the mle-complete
tabulator completion to decide where word boundaries
exist, by default `"'@=;|:' [v15 behaviour may differ]
This mechanism is yet restricted.

line-editor-disable
(Boolean) Turn off any line editing capabilities (from S-
nails POW, see On terminal control and line editor for
more).

line-editor-no-defaults
(Boolean)[Option] Do not establish any default key
binding.

log-prefix Error log message prefix string (`s-nail: ').

mailbox-display
(Read-only) The name of the current mailbox (folder),
possibly abbreviated for display purposes.

mailbox-resolved
(Read-only) The fully resolved path of the current
mailbox.

mailcap-disable
(Boolean)[Option] Turn off consideration of MIME type
handlers from, and implicit loading of The Mailcap files.

mailx-extra-rc
An additional startup file that is loaded as the last of
the Resource files. Use this file for commands that are
not understood by other POSIX mailx(1) implementations,
i.e., mostly anything which is not covered by Initial
settings.

markanswered
(Boolean) When a message is replied to and this variable
is set, it is marked as having been answered. See the
section Message states.

mbox-fcc-and-pcc
(Boolean) By default all file and pipe message receivers
(see expandaddr) will be fed valid MBOX database entry
message data (see folder, mbox-rfc4155), and existing file
targets will become extended in compliance to RFC 4155.
If this variable is unset then a plain standalone RFC 5322
message will be written, and existing file targets will be
overwritten.

mbox-rfc4155
(Boolean) When opening MBOX mailbox databases, and in
order to achieve compatibility with old software, the very
tolerant POSIX standard rules for detecting message
boundaries (so-called `From_' lines) are used instead of
the stricter rules from the standard RFC 4155. This
behaviour can be switched by setting this variable.

This may temporarily be handy when S-nail complains about
invalid `From_' lines when opening a MBOX: in this case
setting this variable and re-opening the mailbox in
question may correct the result. If so, copying the
entire mailbox to some other file, as in `copy *
SOME-FILE', will perform proper, all-compatible `From_'
quoting for all detected messages, resulting in a valid
MBOX mailbox. ([v15 behaviour may differ] The better and
non-destructive approach is to re-encode invalid messages,
as if it would be created anew, instead of mangling the
`From_' lines; this requires the structural code changes
of the v15 rewrite.) Finally the variable can be unset
again:

define mboxfix {
localopts yes; wysh set mbox-rfc4155;\
wysh File "${1}"; copy * "${2}"
}
call mboxfix /tmp/bad.mbox /tmp/good.mbox

memdebug (Boolean) Internal development variable. (Keeps memory
debug enabled even if debug is not set.)

message-id-disable
(Boolean) By setting this variable the generation of
`Message-ID:' and `Content-ID:' message and MIME part
headers can be completely suppressed, effectively leaving
this task up to the mta (Mail-Transfer-Agent) or the SMTP
server. Note that according to RFC 5321 a SMTP server is
not required to add this field by itself, so it should be
ensured that it accepts messages without `Message-ID'.

message-inject-head
A string to put at the beginning of each new message,
followed by a newline. [Obsolete] The escape sequences
tabulator `\t' and newline `\n' are understood (use the
wysh prefix when setting the variable(s) instead).

message-inject-tail
A string to put at the end of each new message, followed
by a newline. [Obsolete] The escape sequences tabulator
`\t' and newline `\n' are understood (use the wysh prefix
when setting the variable(s) instead). Also see
on-compose-leave.

metoo (Boolean) Usually, when an alias expansion contains the
sender, the sender is removed from the expansion. Setting
this option suppresses these removals. Note that a set
metoo also causes a `-m' option to be passed through to
the mta (Mail-Transfer-Agent); though most of the modern
MTAs no longer document this flag, no MTA is known which
does not support it (for historical compatibility).

mime-allow-text-controls
(Boolean) When sending messages, each part of the message
is MIME-inspected in order to classify the `Content-Type:'
and `Content-Transfer-Encoding:' (see mime-encoding) that
is required to send this part over mail transport, i.e., a
computation rather similar to what the file(1) command
produces when used with the `--mime' option.

This classification however treats text files which are
encoded in UTF-16 (seen for HTML files) and similar
character sets as binary octet-streams, forcefully
changing any `text/plain' or `text/html' specification to
`application/octet-stream': If that actually happens a yet
unset charset MIME parameter is set to `binary',
effectively making it impossible for the receiving MUA to
automatically interpret the contents of the part.

If this variable is set, and the data was unambiguously
identified as text data at first glance (by a `.txt' or
`.html' file extension), then the original `Content-Type:'
will not be overwritten.

mime-alternative-favour-rich
(Boolean) If this variable is set then rich MIME
alternative parts (e.g., HTML) will be preferred in favour
of included plain text versions when displaying messages,
provided that a handler exists which produces output that
can be (re)integrated into S-nail's normal visual display.

mime-counter-evidence
Normally the `Content-Type:' field is used to decide how
to handle MIME parts. Some MUAs, however, do not use The
mime.types files (also see HTML mail and MIME attachments)
or a similar mechanism to correctly classify content, but
specify an unspecific MIME type
(`application/octet-stream') even for plain text
attachments. If this variable is set then S-nail will try
to re-classify such MIME message parts, if possible, for
example via a possibly existing attachment filename. A
non-empty value may also be given, in which case a number
is expected, actually a carrier of bits, best specified as
a binary value, like `0b1111'.

+o If bit two is set (counting from 1, decimal 2) then
the detected mimetype will be carried along with the
message and be used for deciding which MIME handler is
to be used, for example; when displaying such a MIME
part the part-info will indicate the overridden
content-type by showing a plus sign `+'.
+o If bit three is set (decimal 4) then the counter-
evidence is always produced and a positive result will
be used as the MIME type, even forcefully overriding
the parts given MIME type.
+o If bit four is set (decimal 8) as a last resort the
actual content of `application/octet-stream' parts
will be inspected, so that data which looks like plain
text can be treated as such. This mode is even more
relaxed when data is to be displayed to the user or
used as a message quote (data consumers which mangle
data for display purposes, which includes masking of
control characters, for example).

mime-encoding
The MIME `Content-Transfer-Encoding' to use in outgoing
text messages and message parts, where applicable (7-bit
clean text messages are without an encoding if possible):

`8bit' (Or `8b'.) 8-bit transport effectively causes
the raw data be passed through unchanged, but
may cause problems when transferring mail
messages over channels that are not ESMTP
(RFC 1869) compliant. Also, several input
data constructs are not allowed by the
specifications and may cause a different
transfer-encoding to be used. By established
rules and popular demand occurrences of
`^From_' (see mbox-rfc4155) will be MBOXO
quoted (prefixed with greater-than sign `>')
instead of causing a non-destructive encoding
like `quoted-printable' to be chosen, unless
context (like message signing) requires
otherwise.
`quoted-printable'
(Or `qp'.) Quoted-printable encoding is 7-bit
clean and has the property that ASCII
characters are passed through unchanged, so
that an english message can be read as-is; it
is also acceptable for other single-byte
locales that share many characters with
ASCII, for example ISO-8859-1. The encoding
will cause a large overhead for messages in
other character sets: for example it will
require up to twelve (12) bytes to encode a
single UTF-8 character of four (4) bytes. It
is the default encoding.
`base64' (Or `b64'.) This encoding is 7-bit clean and
will always be used for binary data. This
encoding has a constant input:output ratio of
3:4, regardless of the character set of the
input data it will encode three bytes of
input to four bytes of output. This
transfer-encoding is not human readable
without performing a decoding step.

mime-force-sendout
(Boolean)[Option] Whenever it is not acceptable to fail
sending out messages because of non-convertible character
content this variable may be set. It will, as a last
resort, classify the part content as
`application/octet-stream'. Please refer to the section
Character sets for the complete picture of character set
conversion, and HTML mail and MIME attachments for how to
internally or externally handle part content.

mimetypes-load-control
Can be used to control which of The mime.types files are
loaded: if the letter `u' is part of the option value,
then the user's personal ~/:.mime.types file will be
loaded (if it exists); likewise the letter `s' controls
loading of the system wide /:etc/:mime.types; directives
found in the user file take precedence, letter matching is
case-insensitive. If this variable is not set S-nail will
try to load both files. Incorporation of the S-nail-
built-in MIME types cannot be suppressed, but they will be
matched last (the order can be listed via mimetype).

More sources can be specified by using a different syntax:
if the value string contains an equals sign `=' then it is
instead parsed as a comma-separated list of the described
letters plus `f=FILENAME' pairs; the given filenames will
be expanded and loaded, and their content may use the
extended syntax that is described in the section The
mime.types files. Directives found in such files always
take precedence (are prepended to the MIME type cache).

mta Select an alternate Mail-Transfer-Agent by either
specifying the full pathname of an executable (a `file://'
prefix may be given), or [Option]ally a SMTP aka
SUBMISSION protocol URL [v15-compat]:

submissions://[user[:password]@]server[:port]

([no v15-compat]: `[smtp://]server[:port]'.) The default
has been chosen at compile time. MTA data transfers are
always performed in asynchronous child processes, and
without supervision unless either the sendwait or the
verbose variable is set. Also see mta-bcc-ok.
[Option]ally expansion of aliases(5) can be performed by
setting mta-aliases.

For testing purposes there is the `test' pseudo-MTA, which
dumps to standard output or optionally to a file, and
honours mbox-fcc-and-pcc:

$ echo text | s-nail -:/ -Smta=test -s ubject ex@am.ple
$ </dev/null s-nail -:/ -Smta=test://./xy ex@am.ple

For a file-based MTA it may be necessary to set mta-argv0
in in order to choose the right target of a modern
mailwrapper(8) environment. It will be passed command
line arguments from several possible sources: from the
variable mta-arguments if set, from the command line if
given and the variable expandargv allows their use.
Argument processing of the MTA will be terminated with a
-- separator.

The otherwise occurring implicit usage of the following
MTA command line arguments can be disabled by setting the
boolean variable mta-no-default-arguments (which will also
disable passing -- to the MTA): -i (for not treating a
line with only a dot `.' character as the end of input),
-m (shall the variable metoo be set) and -v (if the
verbose variable is set); in conjunction with the -r
command line option or r-option-implicit -f as well as
possibly -F will (not) be passed.

[Option]ally S-nail can send mail over SMTP aka SUBMISSION
network connections to a single defined smart host by
setting this variable to a SMTP or SUBMISSION URL (see On
URL syntax and credential lookup). An authentication
scheme can be specified via the variable chain smtp-auth.
Encrypted network connections are [Option]ally available,
the section Encrypted network communication should give an
overview and provide links to more information on this.
Note that with some mail providers it may be necessary to
set the smtp-hostname variable in order to use a specific
combination of from, hostname and mta. Network
communication socket timeouts are configurable via
socket-connect-timeout. All generated network traffic may
be proxied over a SOCKS socks-proxy, it can be logged by
setting verbose twice. The following SMTP variants may be
used:

+o The plain SMTP protocol (RFC 5321) that normally lives
on the server port 25 and requires setting the
smtp-use-starttls variable to enter a TLS encrypted
session state. Assign a value like [v15-compat]
`smtp://[user[:password]@]server[:port]' ([no
v15-compat] `smtp://server[:port]') to choose this
protocol.

+o The so-called SMTPS which is supposed to live on
server port 465 and is automatically TLS secured.
Unfortunately it never became a standardized protocol
and may thus not be supported by your hosts network
service database - in fact the port number has already
been reassigned to other protocols!

SMTPS is nonetheless a commonly offered protocol and
thus can be chosen by assigning a value like
[v15-compat] `smtps://[user[:password]@]server[:port]'
([no v15-compat] `smtps://server[:port]'); due to the
mentioned problems it is usually necessary to
explicitly specify the port as `:465', however.

+o The SUBMISSION protocol (RFC 6409) lives on server
port 587 and is identically to the SMTP protocol from
S-nail's point of view; it requires setting
smtp-use-starttls to enter a TLS secured session
state; e.g., [v15-compat]
`submission://[user[:password]@]server[:port]'.

+o The SUBMISSIONS protocol (RFC 8314) that lives on
server port 465 and is TLS secured by default. It can
be chosen by assigning a value like [v15-compat]
`submissions://[user[:password]@]server[:port]'. Due
to the problems mentioned for SMTPS above and the fact
that SUBMISSIONS is new and a successor that lives on
the same port as the historical engineering
mismanagement named SMTPS, it is usually necessary to
explicitly specify the port as `:465'.

mta-aliases [Option] If set to a path pointing to a text file in valid
MTA (Postfix) aliases(5) format, the file is loaded and
cached (manageable with mtaaliases), and henceforth plain
`name' (see expandaddr) message receiver names are
recursively expanded as a last expansion step, after the
distribution lists which can be created with alias.
Constraints on aliases(5) content support: only local
addresses (names) which are valid usernames
(`[a-z_][a-z0-9_-]*[$]?') are treated as expandable
aliases, and [v15 behaviour may differ]
`:include:/file/name' directives are not supported. By
including `-name' in expandaddr it can be asserted that
only expanded names (mail addresses) are passed through to
the MTA.

mta-arguments
Arguments to pass through to a file-based mta (Mail-
Transfer-Agent), parsed according to Shell-style argument
quoting into an array of arguments which will be joined
onto MTA options from other sources, for example `? wysh
set mta-arguments='-t -X "/tmp/my log"''.

mta-no-default-arguments
(Boolean) Avoids passing standard command line options to
a file-based mta (please see there).

mta-no-receiver-arguments
(Boolean) By default all receiver addresses will be passed
as command line options to a file-based mta. Setting this
variable disables this behaviour to aid those MTAs which
employ special treatment of such arguments. Doing so can
make it necessary to pass a -t via mta-arguments, to
testify the MTA that it should use the passed message as a
template.

mta-argv0 Many systems use a so-called mailwrapper(8) environment to
ensure compatibility with sendmail(1). This works by
inspecting the name that was used to invoke the mail
delivery system. If this variable is set then the
mailwrapper (the program that is actually executed when
calling the file-based mta) will treat its contents as
that name.

mta-bcc-ok (Boolean) In violation of RFC 5322 some MTAs do not remove
`Bcc:' header lines from transported messages after having
noted the respective receivers for addressing purposes.
(The MTAs Exim and Courier for example require the command
line option -t to enforce removal.) Unless this is set
corresponding receivers are addressed by protocol-specific
means or MTA command line options only, the header itself
is stripped before being sent over the wire.

netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup
(Boolean)[v15-compat][Option] Used to control usage of the
user's ~/:.netrc file for lookup of account credentials,
as documented in the section On URL syntax and credential
lookup and for the command netrc; the section The .netrc
file documents the file format. Also see netrc-pipe.

netrc-pipe [v15-compat][Option] When ~/:.netrc is loaded (see netrc
and netrc-lookup) then S-nail will read the output of a
shell pipe instead of the user's ~/:.netrc file if this
variable is set (to the desired shell command). This can
be used to, for example, store ~/:.netrc in encrypted
form: `? set netrc-pipe='gpg -qd ~/.netrc.pgp''.

newfolders [Option] If this variable has the value `maildir', newly
created local folders will be in Maildir instead of MBOX
format.

newmail Checks for new mail in the current folder each time the
prompt is shown. A Maildir folder must be re-scanned to
determine if new mail has arrived. If this variable is
set to the special value `nopoll' then a Maildir folder
will not be rescanned completely, but only timestamp
changes are detected. Maildir folders are [Option]al.

outfolder (Boolean) Causes a non-absolute filename specified in
record, as well as the sender-based filenames of the Copy,
Save, Followup and followup commands to be interpreted
relative to the folder directory rather than relative to
the current directory.

on-account-cleanup-ACCOUNT, on-account-cleanup
Macro hook which will be called once an account is left,
as the very last step before unrolling per-account
localopts. This hook is run even in case of fatal errors,
including those generated by switching to the account as
such, and it is advisable to perform only absolutely
necessary actions, like cleaning up alternates, for
example. The specialized form is used in favour of the
generic one if found.

on-compose-cleanup
Macro hook which will be called after the message has been
sent (or not, in case of failures), as the very last step
before unrolling compose mode localopts. This hook is run
even in case of fatal errors, and it is advisable to
perform only absolutely necessary actions, like cleaning
up alternates, for example.

For compose mode hooks that may affect the message content
please see on-compose-enter, on-compose-leave,
on-compose-splice. [v15 behaviour may differ] This hook
exists because alias, alternates, commandalias, shortcut,
to name a few, are neither covered by localopts nor by
local: changes applied in compose mode will continue to be
in effect thereafter.

on-compose-enter, on-compose-leave
Macro hooks which will be called once compose mode is
entered, and after composing has been finished,
respectively; the exact order of the steps taken is
documented for ~., one of the COMMAND ESCAPES. Context
about the message being worked on can be queried via
digmsg. localopts are enabled for these hooks, and
changes on variables will be forgotten after the message
has been sent. on-compose-cleanup can be used to perform
other necessary cleanup steps.

Here is an example that injects a signature via
message-inject-tail; instead using on-compose-splice to
simply inject the file of desire via ~< or ~<! may be a
better approach.

define t_ocl {
vput ! i cat ~/.mysig
if $? -eq 0
vput csop message-inject-tail trim-end $i
end

# Alternatively
readctl create ~/.mysig
if $? -eq 0
readall i
if $? -eq 0
vput csop message-inject-tail trim-end $i
end
readctl remove ~/.mysig
end
}
set on-compose-leave=t_ocl

on-compose-splice, on-compose-splice-shell
These hooks run once the normal compose mode is finished,
but before the on-compose-leave macro hook is called etc.
Both hooks will be executed in a subprocess, with their
input and output connected to S-nail such that they can
act as if they would be an interactive user. The
difference in between them is that the latter is a SHELL
command, whereas the former is a normal defined macro, but
which is restricted to a small set of commands (the
verbose output of for example list will indicate said
capability). localopts are enabled for these hooks (in
the parent process), causing any setting to be forgotten
after the message has been sent; on-compose-cleanup can be
used to perform other cleanup as necessary.

During execution of these hooks S-nail will temporarily
forget whether it has been started in interactive mode, (a
restricted set of) COMMAND ESCAPES will always be
available, and for guaranteed reproducibilities sake
escape and ifs will be set to their defaults. The compose
mode command ~^ has been especially designed for
scriptability (via these hooks). The first line the hook
will read on its standard input is the protocol version of
said command escape, currently "0 0 2": backward
incompatible protocol changes have to be expected.

Care must be taken to avoid deadlocks and other false
control flow: if both involved processes wait for more
input to happen at the same time, or one does not expect
more input but the other is stuck waiting for consumption
of its output, etc. There is no automatic synchronization
of the hook: it will not be stopped automatically just
because it, e.g., emits `~x'. The hooks will however
receive a termination signal if the parent enters an error
condition. [v15 behaviour may differ] Protection against
and interaction with signals is not yet given; it is
likely that in the future these scripts will be placed in
an isolated session, which is signalled in its entirety as
necessary.

define ocs_signature {
read version
echo '~< ~/.mysig' # '~<! fortune pathtofortunefile'
}
set on-compose-splice=ocs_signature

wysh set on-compose-splice-shell=$'\
read version;\
printf "hello $version! Headers: ";\
echo \'~^header list\';\
read status result;\
echo "status=$status result=$result";\
'

define ocsm {
read version
echo Splice protocol version is $version
echo '~^h l'; read hl; vput csop es subs "${hl}" 0 1
if "$es" != 2
echoerr 'Cannot read header list'; echo '~x'; xit
endif
if "$hl" !%?case ' cc'
echo '~^h i cc "Diet is your <mirr.or>"'; read es;\
vput csop es substring "${es}" 0 1
if "$es" != 2
echoerr 'Cannot insert Cc: header'; echo '~x'
# (no xit, macro finishes anyway)
endif
endif
}
set on-compose-splice=ocsm

on-history-addition
This hook will be called if an entry is about to be added
to the history of the MLE, as documented in On terminal
control and line editor. It will be called with three
arguments: the first is the name of the input context (see
bind), the second is either an empty string or the
matching history-gabby type, and the third being the
complete command line to be added. The entry will not be
added to history if the hook uses a non-0 return. [v15
behaviour may differ] A future version will give the
expanded command name as the third argument, followed by
the tokenized command line as parsed in the remaining
arguments, the first of which is the original unexpanded
command name; i.e., one may do `shift 4' and will then be
able to access the positional parameters as usual via *,
#, 1 etc.

on-main-loop-tick
This hook will be called whenever the program's main event
loop is about to read the next input line. Note variable
and other changes it performs are not scoped as via
localopts!

on-program-exit
This hook will be called when the program exits, whether
via exit or quit, or because the send mode is done. Note:
this runs late and so terminal settings etc. are already
teared down.

on-resend-cleanup
[v15 behaviour may differ] Identical to
on-compose-cleanup, but is only triggered by resend.

on-resend-enter
[v15 behaviour may differ] Identical to on-compose-enter,
but is only triggered by resend; currently there is no
digmsg support, for example.

page (Boolean) If set, each message feed through the command
given for pipe is followed by a formfeed character `\f'.

password-USER@HOST, password-HOST, password
[v15-compat] Variable chain that sets a password, which is
used in case none has been given in the protocol and
account-specific URL; as a last resort S-nail will ask for
a password on the user's terminal if the authentication
method requires a password. Specifying passwords in a
startup file is generally a security risk; the file should
be readable by the invoking user only.

password-USER@HOST
[no v15-compat] (see the chain above for [v15-compat]) Set
the password for `USER' when connecting to `HOST'. If no
such variable is defined for a host, the user will be
asked for a password on standard input. Specifying
passwords in a startup file is generally a security risk;
the file should be readable by the invoking user only.

piperaw (Boolean) Send messages to the pipe command without
performing MIME and character set conversions.

pipe-EXTENSION
Identical to pipe-TYPE/SUBTYPE except that `EXTENSION'
(normalized to lowercase using character mappings of the
ASCII charset) denotes a file extension, for example
`xhtml'. Handlers registered using this method take
precedence.

pipe-TYPE/SUBTYPE
A MIME message part identified as `TYPE/SUBTYPE' (case-
insensitive, normalized to lowercase using character
mappings of the ASCII charset) is displayed or quoted, its
text is filtered through the value of this variable
interpreted as a shell command. Unless noted only parts
displayable as inline plain text (see copiousoutput) are
covered, other MIME parts will only be considered by and
for mimeview.

The special value question mark `?' forces interpretation
of the message part as plain text, for example `set
pipe-application/xml=?'. (This can also be achieved by
adding a MIME type-marker via mimetype.) [Option]ally MIME
type handlers may be defined via The Mailcap files to
which should be referred to for documentation of flags
like copiousoutput. Question mark is indeed a trigger
character to indicate flags that adjust behaviour and
usage of the rest of the value, the shell command, for
example:

? set pipe-X/Y='?!++=? vim ${MAILX_FILENAME_TEMPORARY}'

`*' The command output can be reintegrated into
this MUA's normal processing: copiousoutput.
Implied when using a plain `'.
`#' Only use this handler for display, not for
quoting a message: x-mailx-noquote.
`&' Run the command asynchronously, do not wait for
the handler to exit: x-mailx-async. The
standard output of the command will go to
/dev/null.
`!' The command must be run on an interactive
terminal, the terminal will temporarily be
released for it to run: needsterminal.
`+' Request creation of a zero-sized temporary
file, the absolute pathname of which will be
made accessible via the environment variable
MAILX_FILENAME_TEMPORARY: x-mailx-tmpfile. If
given twice then the file will be unlinked
automatically by S-nail when the command loop
is entered again at latest:
x-mailx-tmpfile-unlink; it is an error to use
automatic deletion in conjunction with
x-mailx-async.
`=' Normally the MIME part content is passed to the
handler via standard input; with this the data
will instead be written into
MAILX_FILENAME_TEMPORARY
(x-mailx-tmpfile-fill), the creation of which
is implied; in order to cause automatic
deletion of the temporary file two plus signs
`++' still have to be used.
`t' Text type-marker: display this as normal plain
text (for type-markers: The mime.types files).
Identical to only giving plain `?', implies
copiousoutput.
`h' [Option] HTML type-marker: display via built-in
HTML-to-text filter. Implies copiousoutput.
`?' To avoid ambiguities with normal shell command
content another question mark can be used to
forcefully terminate interpretation of
remaining characters. (Any character not in
this list will have the same effect.)

Some information about the MIME part to be displayed is
embedded into the environment of the shell command:

MAILX_CONTENT The MIME content-type of
the part, if known, the
empty string otherwise.
MAILX_CONTENT_EVIDENCE If mime-counter-evidence
includes the carry-around-
bit (2), then this will be
set to the detected MIME
content-type; not only
then identical to
MAILX_CONTENT otherwise.
MAILX_EXTERNAL_BODY_URL MIME parts of type
`message/external-body
access-type=url' will
store the access URL in
this variable, it is empty
otherwise. URL targets
should not be activated
automatically, without
supervision.
MAILX_FILENAME The filename, if any is
set, the empty string
otherwise.
MAILX_FILENAME_GENERATED A random string.
MAILX_FILENAME_TEMPORARY If temporary file creation
has been requested through
the command prefix this
variable will be set and
contain the absolute
pathname of the temporary
file.

pop3-auth-USER@HOST, pop3-auth-HOST, pop3-auth
[Option][v15-compat] Variable chain that sets the POP3
authentication method. Supported are the default `plain',
[v15-compat] `oauthbearer' (see FAQ entry But, how about
XOAUTH2 / OAUTHBEARER?), as well as [v15-compat]
`external' and `externanon' for TLS secured connections
which pass a client certificate via tls-config-pairs.
There may be the [Option]al method [v15-compat] `gssapi'.
`externanon' does not need any user credentials,
`external' and `gssapi' need a user, the remains also
require a password. `externanon' solely builds upon the
credentials passed via a client certificate, and is
usually the way to go since tested servers do not actually
follow RFC 4422, and fail if additional credentials are
actually passed. Unless pop3-no-apop is set the `plain'
method will [Option]ally be replaced with APOP if possible
(see there).

pop3-bulk-load-USER@HOST, pop3-bulk-load-HOST, pop3-bulk-load
(Boolean)[Option] When accessing a POP3 server S-nail
loads the headers of the messages, and only requests the
message bodies on user request. For the POP3 protocol
this means that the message headers will be downloaded
twice. If this variable is set then S-nail will download
only complete messages from the given POP3 server(s)
instead.

pop3-keepalive-USER@HOST, pop3-keepalive-HOST, pop3-keepalive
[Option] POP3 servers close the connection after a period
of inactivity; the standard requires this to be at least
10 minutes, but practical experience may vary. Setting
this variable to a numeric value greater than `0' causes a
`NOOP' command to be sent each value seconds if no other
operation is performed.

pop3-no-apop-USER@HOST, pop3-no-apop-HOST, pop3-no-apop
(Boolean)[Option] Unless this variable is set the MD5
based `APOP' authentication method will be used instead of
a chosen `plain' pop3-auth when connecting to a POP3
server that advertises support. The advantage of `APOP'
is that only a single packet is sent for the user/password
tuple. (Originally also that the password is not sent in
clear text over the wire, but for one MD5 does not any
longer offer sufficient security, and then today transport
is almost ever TLS secured.) Note that pop3-no-apop-HOST
requires [v15-compat].

pop3-use-starttls-USER@HOST, pop3-use-starttls-HOST, pop3-use-starttls
(Boolean)[Option] Causes S-nail to issue a `STLS' command
to make an unencrypted POP3 session TLS encrypted. This
functionality is not supported by all servers, and is not
used if the session is already encrypted by the POP3S
method. Note that pop3-use-starttls-HOST requires
[v15-compat].

posix (Boolean) This flag enables POSIX mode, which changes
behaviour of S-nail where that deviates from standardized
behaviour. It is automatically squared with the
environment variable POSIXLY_CORRECT, changing the one
will adjust the other. The following behaviour is covered
and enforced by this mechanism:

+o In non-interactive mode, any error encountered while
loading resource files during program startup will
cause a program exit, whereas in interactive mode such
errors will stop loading of the currently loaded
(stack of) file(s, i.e., recursively). These exits
can be circumvented on a per-command base by using
ignerr, one of the Command modifiers, for each command
which shall be allowed to fail.
+o alternates will replace the list of alternate
addresses instead of appending to it. In addition
alternates will only be honoured for any sort of
message reply, and for aliases.
+o The variable inserting COMMAND ESCAPES ~A, ~a, ~I and
~i will expand embedded character sequences `\t'
horizontal tabulator and `\n' line feed. [v15
behaviour may differ] For compatibility reasons this
step will always be performed.
+o Reading in messages via ~f (COMMAND ESCAPES) will use
the `type' not the `forward' headerpick selection.
+o Upon changing the active folder no summary of headers
will be displayed even if header is set.
+o Setting ignoreeof implies the behaviour described by
dot.
+o The variable keep is extended to cover any empty
mailbox, not only empty primary system mailboxes: they
will be removed when they are left in empty state
otherwise.
+o Each command has an exit ? and error ! status that
overwrites that of the last command. In POSIX mode
the program exit status will signal failure regardless
unless all messages were successfully sent out to the
mta; also see sendwait.

print-alternatives
(Boolean) When a MIME message part of type
`multipart/alternative' is displayed and it contains a
subpart of type `text/plain', other parts are normally
discarded. Setting this variable causes all subparts to
be displayed, just as if the surrounding part was of type
`multipart/mixed'.

prompt The string used as a prompt in interactive mode. Whenever
the variable is evaluated the value is treated as if
specified within dollar-single-quotes (see Shell-style
argument quoting). This (post-assignment, i.e., second)
expansion can be used to embed status information, for
example ?, !, account or mailbox-display.

In order to embed characters which should not be counted
when calculating the visual width of the resulting string,
enclose the characters of interest in a pair of reverse
solidus escaped brackets: `\[\E[0m\]'; a slot for coloured
prompts is also available with the [Option]al command
colour. Prompting may be prevented by setting this to the
null string (aka `set noprompt').

prompt2 This string is used for secondary prompts, but is
otherwise identical to prompt. The default is `.. '.

quiet (Boolean) Suppresses the printing of the version when
first invoked.

quote If set messages processed by variants of followup and
reply will start with the original message, lines of which
prefixed by indentprefix, taking into account quote-chars
and quote-fold. No headers will be quoted when set
without value or for `noheading', for `headers' the `type'
headerpick selection will be included in the quote,
`allbodies' embeds the (body) contents of all MIME parts,
and `allheaders' also includes all headers. The quoted
message will be enclosed by the expansions of
quote-inject-head and quote-inject-tail. Also see
quote-add-cc, quote-as-attachment and ~Q, one of the
COMMAND ESCAPES.

quote-add-cc
(Boolean) Whether senders of messages quoted via ~Q shall
be made members of the carbon copies `Cc:' list.

quote-as-attachment
(Boolean) Add the original message in its entirety as a
`message/rfc822' MIME attachment when replying to a
message. Note this works regardless of the setting of
quote.

quote-chars Can be set to a string consisting of non-whitespace ASCII
characters which shall be treated as quotation leaders,
the default being `>|}:'.

quote-fold [Option] Can be set in addition to indentprefix, and
creates a more fancy quotation in that leading quotation
characters (quote-chars) are compressed and overlong lines
are folded. quote-fold can be set to either one, two or
three (space separated) numeric values, which are
interpreted as the maximum (goal) and the minimum line
length, respectively, in a spirit rather equal to the
fmt(1) program, but line- instead of paragraph-based. The
third value is used as the maximum line length instead of
the first if no better break point can be found; it is
ignored unless it is larger than the minimum and smaller
than the maximum. If not set explicitly the minimum will
reflect the goal algorithmically. The goal cannot be
smaller than the length of indentprefix plus some
additional pad; necessary adjustments take place silently.

quote-inject-head, quote-inject-tail
The strings to put before and after the text of a quoted
message, if non-empty, and respectively. The former
defaults to `%f wrote:\n\n'. Special format directives
will be expanded if possible, and if so configured the
output will be folded according to quote-fold. Format
specifiers in the given strings start with a percent sign
`%' and expand values of the original message, unless
noted otherwise. Note that names and addresses are not
subject to the setting of showto. Valid format specifiers
are:

`%%' A plain percent sign.
`%a' The address(es) of the sender(s).
`%d' The date found in the `Date:' header of the
message when datefield is set (the default),
otherwise the date when the message was
received. Formatting can be controlled by
assigning a strftime(3) format string to
datefield (and datefield-markout-older).
`%f' The full name(s) (name and address, as given)
of the sender(s).
`%i' The `Message-ID:'.
`%n' The real name(s) of the sender(s) if there is
one and showname allows usage, the
address(es) otherwise.
`%r' The senders real name(s) if there is one, the
address(es) otherwise.

r-option-implicit
(Boolean) Setting this option evaluates the contents of
from (or, if that contains multiple addresses, sender) and
passes the results onto the used (file-based) MTA as
described for the -r option (empty argument case).

recipients-in-cc
(Boolean) When doing a reply, the original `From:' and
`To:' as well as addressees which possibly came in via
`Reply-To:' and `Mail-Followup-To:' are by default merged
into the new `To:'. If this variable is set a sensitive
algorithm tries to place in `To:' only the sender of the
message being replied to, others are placed in `Cc:'.

record Unless this variable is defined, no copies of outgoing
mail will be saved. If defined it gives the pathname,
subject to the usual Filename transformations, of a folder
where all new, replied-to or forwarded messages are saved:
when saving to this folder fails the message is not sent,
but instead saved to DEAD. The standard defines that
relative (fully expanded) paths are to be interpreted
relative to the current directory (cwd), to force
interpretation relative to folder outfolder needs to be
set in addition.

record-files
(Boolean) If this variable is set the meaning of record
will be extended to cover messages which target only file
and pipe recipients (see expandaddr). These address types
will not appear in recipient lists unless
add-file-recipients is also set.

record-resent
(Boolean) If this variable is set the meaning of record
will be extended to also cover the resend and Resend
commands.

reply-in-same-charset
(Boolean) If this variable is set S-nail first tries to
use the same character set of the original message for
replies. If this fails, the mechanism described in
Character sets is evaluated as usual.

reply-strings
Can be set to a comma-separated list of (case-insensitive
according to ASCII rules) strings which shall be
recognized in addition to the built-in strings as
`Subject:' reply message indicators - built-in are `Re:',
which is mandated by RFC 5322, as well as the german
`Aw:', `Antw:', and the `Wg:' which often has been seen in
the wild; I.e., the separating colon has to be specified
explicitly.

reply-to A list of addresses to put into the `Reply-To:' field of
the message header. Members of this list are handled as
if they were in the alternates list.

replyto [Obsolete] Variant of reply-to.

reply-to-honour
Controls whether a `Reply-To:' header is honoured when
replying to a message via reply or Lreply. This is a
quadoption; if set without a value it defaults to "yes".

reply-to-swap-in
Standards like DKIM and (in conjunction with) DMARC caused
many Mailing lists to use sender address rewriting in the
style of `Name via List <list@address>', where the
original sender address often being placed in `Reply-To:'.
If this is set and a `Reply-To:' exists, and consists of
only one addressee (!), then that is used in place of the
pretended sender. This works independently from
reply-to-honour. The optional value, a comma-separated
list of strings, offers more fine-grained control on when
swapping shall be used; for now supported is mlist, here
swapping occurs if the sender is a mailing-list as defined
by mlist.

rfc822-body-from_
(Boolean) This variable can be used to force displaying a
so-called `From_' line for messages that are embedded into
an envelope mail via the `message/rfc822' MIME mechanism,
for more visual convenience, also see mbox-rfc4155.

save (Boolean) Enable saving of (partial) messages in DEAD upon
interrupt or delivery error.

screen The number of lines that represents a "screenful" of
lines, used in headers summary display, from searching,
message topline display and scrolling via z. If this
variable is not set S-nail falls back to a calculation
based upon the detected terminal window size and the baud
rate: the faster the terminal, the more will be shown.
Overall screen dimensions and pager usage is influenced by
the environment variables COLUMNS and LINES and the
variable crt.

searchheaders
(Boolean) Expand message list specifiers in the form
`/x:y' to all messages containing the substring "y" in the
header field `x'. The string search is case insensitive.

sendcharsets
[Option] A comma-separated list of character set names
that can be used in outgoing internet mail. The value of
the variable charset-8bit is automatically appended to
this list of character sets. If no character set
conversion capabilities are compiled into S-nail then the
only supported charset is ttycharset. Also see
sendcharsets-else-ttycharset and refer to the section
Character sets for the complete picture of character set
conversion in S-nail.

sendcharsets-else-ttycharset
(Boolean)[Option] If this variable is set, but
sendcharsets is not, then S-nail acts as if sendcharsets
had been set to the value of the variable ttycharset. In
effect this combination passes through the message data in
the character set of the current locale encoding:
therefore mail message text will be (assumed to be) in
ISO-8859-1 encoding when send from within a ISO-8859-1
locale, and in UTF-8 encoding when send from within an
UTF-8 locale.

The 8-bit fallback charset-8bit never comes into play as
ttycharset is implicitly assumed to be 8-bit and capable
to represent all files the user may specify (as is the
case when no character set conversion support is available
in S-nail and the only supported character set is
ttycharset, see Character sets). This might be a problem
for scripts which use the suggested `LC_ALL=C' setting,
since in this case the character set is US-ASCII by
definition, so that it is better to also override
ttycharset, then; and/or do something like the following
in the resource file:

# Avoid ASCII "propagates to 8-bit" when scripting
\if ! t && "$LC_ALL" != C && "$LC_CTYPE" != C
\set sendcharsets-else-ttycharset
\end

sender An address that is put into the `Sender:' field of
outgoing messages, quoting RFC 5322: the mailbox of the
agent responsible for the actual transmission of the
message. This field should normally not be used unless
the from field contains more than one address, on which
case it is required. [v15 behaviour may differ] Please
expect automatic management of the from and sender
relationship. Dependent on the context this address is
handled as if it were in the list of alternates. Also see
-r, r-option-implicit.

sendmail [Obsolete] Predecessor of mta.

sendmail-arguments
[Obsolete] Predecessor of mta-arguments.

sendmail-no-default-arguments
[Obsolete](Boolean) Predecessor of
mta-no-default-arguments.

sendmail-progname
[Obsolete] Predecessor of mta-argv0.

sendwait Sending messages to the chosen mta or to command-pipe
receivers (see On sending mail, and non-interactive mode)
will be performed asynchronously. This means that only
startup errors of the respective program will be
recognizable, but no delivery errors. Also, no guarantees
can be made as to when the respective program will
actually run, as well as to when they will have produced
output.

If this variable is set then child program exit is waited
for, and its exit status code is used to decide about
success. Remarks: in conflict with the POSIX standard
this variable is built-in to be initially set. Another
difference is that it can have a value, which is
interpreted as a comma-separated list of case-insensitive
strings naming specific subsystems for which
synchronousness shall be ensured (only). Possible values
are `mta' for mta delivery, and `pcc' for command-pipe
receivers.

showlast (Boolean) This setting causes S-nail to start at the last
message instead of the first one when opening a mail
folder, as well as with from and headers.

showname (Boolean) Causes S-nail to use the sender's real name
instead of the plain address in the header field summary
and in message specifications.

showto (Boolean) Causes the recipient of the message to be shown
in the header summary if the message was sent by the user.

Sign The value backing ~A, one of the COMMAND ESCAPES. Also
see message-inject-tail, on-compose-leave and
on-compose-splice.

sign The value backing ~a, one of the COMMAND ESCAPES. Also
see message-inject-tail, on-compose-leave and
on-compose-splice.

signature [Obsolete] Please use on-compose-splice or
on-compose-splice-shell or on-compose-leave and (if
necessary) message-inject-tail instead!

skipemptybody
(Boolean) If an outgoing message has an empty first or
only message part, do not send, but discard it,
successfully (also see the command line option -E).

smime-ca-dir, smime-ca-file
[Option] Specify the location of trusted CA certificates
in PEM (Privacy Enhanced Mail) for the purpose of
verification of S/MIME signed messages. tls-ca-dir
documents the necessary preparation steps to use the
former. The set of CA certificates which are built into
the TLS library can be explicitly turned off by setting
smime-ca-no-defaults, and further fine-tuning is possible
via smime-ca-flags.

smime-ca-flags
[Option] Can be used to fine-tune behaviour of the X509 CA
certificate storage, and the certificate verification that
is used. The actual values and their meanings are
documented for tls-ca-flags.

smime-ca-no-defaults
(Boolean)[Option] Do not load the default CA locations
that are built into the used to TLS library to verify
S/MIME signed messages.

smime-cipher-USER@HOST, smime-cipher
[Option] Specifies the cipher to use when generating
S/MIME encrypted messages (for the specified account).
RFC 5751 mandates a default of `aes128' (AES-128 CBC).
Possible values are (case-insensitive and) in decreasing
cipher strength: `aes256' (AES-256 CBC), `aes192' (AES-192
CBC), `aes128' (AES-128 CBC), `des3' (DES EDE3 CBC, 168
bits; default if `aes128' is not available) and `des' (DES
CBC, 56 bits).

The actually available cipher algorithms depend on the
cryptographic library that S-nail uses. [Option] Support
for more cipher algorithms may be available through
dynamic loading via EVP_get_cipherbyname(3) (OpenSSL) if
S-nail has been compiled to support this.

smime-crl-dir
[Option] Specifies a directory that contains files with
CRLs in PEM format to use when verifying S/MIME messages.

smime-crl-file
[Option] Specifies a file that contains a CRL in PEM
format to use when verifying S/MIME messages.

smime-encrypt-USER@HOST
[Option] If this variable is set, messages send to the
given receiver are encrypted before sending. The value of
the variable must be set to the name of a file that
contains a certificate in PEM format.

If a message is sent to multiple recipients, each of them
for whom a corresponding variable is set will receive an
individually encrypted message; other recipients will
continue to receive the message in plain text unless the
smime-force-encryption variable is set. It is recommended
to sign encrypted messages, i.e., to also set the
smime-sign variable. content-description-smime-message
will be inspected for messages which become encrypted.

smime-force-encryption
(Boolean)[Option] Causes S-nail to refuse sending
unencrypted messages.

smime-sign (Boolean)[Option] S/MIME sign outgoing messages with the
user's (from) private key and include the users
certificate as a MIME attachment. Signing a message
enables a recipient to verify that the sender used a valid
certificate, that the email addresses in the certificate
match those in the message header and that the message
content has not been altered. It does not change the
message text, and people will be able to read the message
as usual. content-description-smime-signature will be
inspected. Also see smime-sign-cert,
smime-sign-include-certs and smime-sign-digest.

smime-sign-cert-USER@HOST, smime-sign-cert
[Option] Points to a file in PEM format. For the purpose
of signing and decryption this file needs to contain the
user's private key, followed by his certificate.

For message signing `USER@HOST' is always derived from the
value of from (or, if that contains multiple addresses,
sender). For the purpose of encryption the recipients
public encryption key (certificate) is expected; the
command certsave can be used to save certificates of
signed messages (the section Signed and encrypted messages
with S/MIME gives some details). This mode of operation
is usually driven by the specialized form.

When decrypting messages the account is derived from the
recipient fields (`To:' and `Cc:') of the message, which
are searched for addresses for which such a variable is
set. S-nail always uses the first address that matches,
so if the same message is sent to more than one of the
user addresses using different encryption keys, decryption
might fail.

Password-encrypted keys may be used for signing and
decryption. Automated password lookup is possible via the
"pseudo-hosts" `USER@HOST.smime-cert-key' for the private
key, and `USER@HOST.smime-cert-cert' for the certificate
stored in the same file. For example, the hypothetical
address `bob@exam.ple' could be driven with a private key
/ certificate pair path defined in
smime-sign-cert-bob@exam.ple, and the needed passwords
would then be looked up as `bob@exam.ple.smime-cert-key'
and `bob@exam.ple.smime-cert-cert'. When decrypting the
value of from will be tried as a fallback to provide the
necessary `USER@HOST'. To include intermediate
certificates, use smime-sign-include-certs. The possible
password sources are documented in On URL syntax and
credential lookup.

smime-sign-digest-USER@HOST, smime-sign-digest
[Option] Specifies the message digest to use when signing
S/MIME messages. Please remember that for this use case
`USER@HOST' refers to the variable from (or, if that
contains multiple addresses, sender). The available
algorithms depend on the used cryptographic library, but
at least one usable built-in algorithm is ensured as a
default. If possible the standard RFC 5751 will be
violated by using `SHA512' instead of the mandated `SHA1'
due to security concerns. This variable is ignored for
very old (released before 2010) cryptographic libraries
which do not offer the necessary interface: it will be
logged if that happened.

S-nail will try to add built-in support for the following
message digests, names are case-insensitive: `BLAKE2b512',
`BLAKE2s256', `SHA3-512', `SHA3-384', `SHA3-256',
`SHA3-224', as well as the widely available `SHA512',
`SHA384', `SHA256', `SHA224', and the proposed insecure
`SHA1', finally `MD5'. More digests may [Option]ally be
available through dynamic loading via the OpenSSL function
EVP_get_digestbyname(3).

smime-sign-include-certs-USER@HOST, smime-sign-include-certs
[Option] If used, this is supposed to a consist of a
comma-separated list of files, each of which containing a
single certificate in PEM format to be included in the
S/MIME message in addition to the smime-sign-cert
certificate. This can be used to include intermediate
certificates of the certificate authority, in order to
allow the receiver's S/MIME implementation to perform a
verification of the entire certificate chain, starting
from a local root certificate, over the intermediate
certificates, down to the smime-sign-cert. Even though
top level certificates may also be included in the chain,
they will not be used for the verification on the
receiver's side.

For the purpose of the mechanisms involved here,
`USER@HOST' refers to the content of the internal variable
from (or, if that contains multiple addresses, sender).
The pseudo-host `USER@HOST.smime-include-certs' will be
used for performing password lookups for these
certificates, shall they have been given one, therefore
the lookup can be automated via the mechanisms described
in On URL syntax and credential lookup.

smime-sign-message-digest-USER@HOST, smime-sign-message-digest
[Obsolete][Option] Predecessor(s) of smime-sign-digest.

smtp [Obsolete][Option] To use the built-in SMTP transport,
specify a SMTP URL in mta. [v15 behaviour may differ] For
compatibility reasons a set smtp is used in preference of
mta.

smtp-auth-USER@HOST, smtp-auth-HOST, smtp-auth
[Option] Variable chain that controls the SMTP mta
authentication method, possible values are `none' ([no
v15-compat] default), `plain' ([v15-compat] default),
`login', [v15-compat] `oauthbearer' (see FAQ entry But,
how about XOAUTH2 / OAUTHBEARER?) as well as [v15-compat]
`external' and `externanon' for TLS secured connections
which pass a client certificate via tls-config-pairs.
There may be the [Option]al methods `cram-md5' and
`gssapi'. `none' and `externanon' do not need any user
credentials, `external' and `gssapi' require a user name,
and all other methods require a user name and a password.
`externanon' solely builds upon the credentials passed via
a client certificate, and is usually the way to go since
tested servers do not actually follow RFC 4422 aka RFC
4954, and fail if additional credentials are passed. Also
see mta. Note that smtp-auth-HOST is [v15-compat]. ([no
v15-compat] Requires smtp-auth-password and
smtp-auth-user. Note for smtp-auth-USER@HOST: may
override dependent on sender address in the variable
from.)

smtp-auth-password
[Option][no v15-compat] Sets the global fallback password
for SMTP authentication. If the authentication method
requires a password, but neither smtp-auth-password nor a
matching smtp-auth-password-USER@HOST can be found, S-nail
will ask for a password on the user's terminal.

smtp-auth-password-USER@HOST
[no v15-compat] Overrides smtp-auth-password for specific
values of sender addresses, dependent upon the variable
from.

smtp-auth-user
[Option][no v15-compat] Sets the global fallback user name
for SMTP authentication. If the authentication method
requires a user name, but neither smtp-auth-user nor a
matching smtp-auth-user-USER@HOST can be found, S-nail
will ask for a user name on the user's terminal.

smtp-auth-user-USER@HOST
[no v15-compat] Overrides smtp-auth-user for specific
values of sender addresses, dependent upon the variable
from.

smtp-hostname
[Option][v15-compat] Normally S-nail uses the variable
from to derive the necessary `USER@HOST' information in
order to issue a `MAIL FROM:<>' SMTP mta command. Setting
smtp-hostname can be used to use the `USER' from the SMTP
account (mta or the user variable chain) and the given
`HOST' (hostname if the empty string is given, or the
local hostname as a last resort). This often allows using
an address that is itself valid but hosted by a provider
other than from which (in from) the message is sent.
Setting this variable also influences generated
`Message-ID:' and `Content-ID:' header fields. If the
[Option]al IDNA support is available (see idna-disable)
variable assignment is aborted when a necessary conversion
fails.

smtp-use-starttls-USER@HOST, smtp-use-starttls-HOST, smtp-use-starttls
(Boolean)[Option] Causes S-nail to issue a `STARTTLS'
command to make an SMTP mta session TLS encrypted, i.e.,
to enable transport layer security.

socket-connect-timeout
[Option] A positive number that defines the timeout to
wait for establishing a socket connection before forcing
^ERR-TIMEDOUT.

socks-proxy-USER@HOST, socks-proxy-HOST, socks-proxy
[Option] If set to the URL of a SOCKS5 server then all
network activities are proxied through it, except for the
single DNS name lookup necessary to resolve the proxy URL
(unnecessary when given an already resolved IP address).
It is automatically squared with the environment variable
SOCKS5_PROXY, changing the one will adjust the other.
This example creates a local SOCKS5 proxy on port 10000
that forwards to the machine `HOST' (with identity
`USER'), and from which actual network traffic happens:

$ ssh -D 10000 USER@HOST
$ s-nail -Ssocks-proxy=[socks5://]localhost:10000
# or =localhost:10000; no local DNS: =127.0.0.1:10000

spam-interface
[Option] In order to use any of the spam-related commands
(like spamrate) the desired spam interface must be defined
by setting this variable. Please refer to the manual
section Handling spam for the complete picture of spam
handling in S-nail. All or none of the following
interfaces may be available:

`spamc' Interaction with spamc(1) from the
spamassassin(1) (SpamAssassin:
http://spamassassin.apache.org) suite.
Different to the generic filter interface
S-nail will automatically add the correct
arguments for a given command and has the
necessary knowledge to parse the program's
output. A default value for spamc-command
will have been compiled into the S-nail
binary if spamc(1) has been found in PATH
during compilation. Shall it be necessary
to define a specific connection type
(rather than using a configuration file for
that), the variable spamc-arguments can be
used as in for example `-d
server.example.com -p 783'. It is also
possible to specify a per-user
configuration via spamc-user. Note that
this interface does not inspect the
`is-spam' flag of a message for the command
spamforget.

`filter' generic spam filter support via freely
configurable hooks. This interface is
meant for programs like bogofilter(1) and
requires according behaviour in respect to
the hooks' exit status for at least the
command spamrate (`0' meaning a message is
spam, `1' for non-spam, `2' for unsure and
any other return value indicating a hard
error); since the hooks can include shell
code snippets diverting behaviour can be
intercepted as necessary. The hooks are
spamfilter-ham, spamfilter-noham,
spamfilter-nospam, spamfilter-rate and
spamfilter-spam; the manual section
Handling spam contains examples for some
programs. The process environment of the
hooks will have the variable
MAILX_FILENAME_GENERATED set. Note that
spam score support for spamrate is not
supported unless the [Option]tional regular
expression support is available and the
spamfilter-rate-scanscore variable is set.

spam-maxsize
[Option] Messages that exceed this size will not be passed
through to the configured spam-interface. If unset or 0,
the default of 420000 bytes is used.

spamc-command
[Option] The path to the spamc(1) program for the `spamc'
spam-interface. Note that the path is not expanded, but
used "as is". A fallback path will have been compiled
into the S-nail binary if the executable had been found
during compilation.

spamc-arguments
[Option] Even though S-nail deals with most arguments for
the `spamc' spam-interface automatically, it may at least
sometimes be desirable to specify connection-related ones
via this variable, for example `-d server.example.com -p
783'.

spamc-user [Option] Specify a username for per-user configuration
files for the `spamc' spam-interface. If this is set to
the empty string then S-nail will use the name of the
current user.

spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate,
spamfilter-spam
[Option] Command and argument hooks for the `filter'
spam-interface. The manual section Handling spam contains
examples for some programs.

spamfilter-rate-scanscore
[Option] Because of the generic nature of the `filter'
spam-interface spam scores are not supported for it by
default, but if the [Option]nal regular expression support
is available then setting this variable can be used to
overcome this restriction. It is interpreted as follows:
first a number (digits) is parsed that must be followed by
a semicolon `;' and an extended regular expression. Then
the latter is used to parse the first output line of the
spamfilter-rate hook, and, in case the evaluation is
successful, the group that has been specified via the
number is interpreted as a floating point scan score.

ssl-ca-dir-USER@HOST, ssl-ca-dir-HOST, ssl-ca-dir,
ssl-ca-file-USER@HOST, ssl-ca-file-HOST, ssl-ca-file
[Obsolete][Option] Predecessors of tls-ca-file,
tls-ca-dir.

ssl-ca-flags-USER@HOST, ssl-ca-flags-HOST, ssl-ca-flags
[Obsolete][Option] Predecessor of tls-ca-flags.

ssl-ca-no-defaults-USER@HOST, ssl-ca-no-defaults-HOST,
ssl-ca-no-defaults
[Obsolete](Boolean)[Option] Predecessor of
tls-ca-no-defaults.

ssl-cert-USER@HOST, ssl-cert-HOST, ssl-cert
[Obsolete][Option] Please use the Certificate slot of
tls-config-pairs.

ssl-cipher-list-USER@HOST, ssl-cipher-list-HOST, ssl-cipher-list
[Obsolete][Option] Please use the CipherString slot of
tls-config-pairs.

ssl-config-file
[Obsolete][Option] Predecessor of tls-config-file.

ssl-config-module-USER@HOST, ssl-config-module-HOST, ssl-config-module
[Obsolete][Option] Predecessor of tls-config-module.

ssl-config-pairs-USER@HOST, ssl-config-pairs-HOST, ssl-config-pairs
[Obsolete][Option] Predecessor of tls-config-pairs.

ssl-crl-dir, ssl-crl-file
[Obsolete][Option] Predecessors of tls-crl-dir,
tls-crl-file.

ssl-curves-USER@HOST, ssl-curves-HOST, ssl-curves
[Obsolete][Option] Please use the Curves slot of
tls-config-pairs.

ssl-features
[Obsolete][Option](Read-only) Predecessor of tls-features.

ssl-key-USER@HOST, ssl-key-HOST, ssl-key
[Obsolete][Option] Please use the PrivateKey slot of
tls-config-pairs.

ssl-method-USER@HOST, ssl-method-HOST, ssl-method
[Obsolete][Option] Please use the Protocol slot of
tls-config-pairs.

ssl-protocol-USER@HOST, ssl-protocol-HOST, ssl-protocol
[Obsolete][Option] Please use the Protocol slot of
tls-config-pairs.

ssl-rand-file
[Obsolete][Option] Predecessor of tls-rand-file.

ssl-verify-USER@HOST, ssl-verify-HOST, ssl-verify
[Obsolete][Option] Predecessor of tls-verify.

stealthmua If only set without an assigned value, then this setting
inhibits the generation of the `Message-ID:',
`Content-ID:' and `User-Agent:' header fields that include
obvious references to S-nail. There are two pitfalls
associated with this: First, the message id of outgoing
messages is not known anymore. Second, an expert may
still use the remaining information in the header to track
down the originating mail user agent. If set to the value
`noagent', then the mentioned `Message-ID:' and
`Content-ID:' suppression does not occur.

system-mailrc
(Read-only) The compiled in path of the system wide
initialization file one of the Resource files: s-nail.rc.

termcap ([Option]) This specifies a comma-separated list of
library "libterminfo" and/or library "libtermcap"
capabilities (see On terminal control and line editor,
escape commas with reverse solidus `\') to be used to
overwrite or define entries. Note this variable will only
be queried once at program startup and can thus only be
specified in resource files or on the command line. It
will always be inspected, regardless of whether features
denotes termcap/terminfo library support via `,+termcap,'.

String capabilities form `cap=value' pairs and are
expected unless noted otherwise. Numerics have to be
notated as `cap#number' where the number is expected in
normal decimal notation. Finally, booleans do not have
any value but indicate a true or false state simply by
being defined or not; this indeed means that S-nail does
not support undefining an existing boolean. String
capability values will undergo some expansions before use:
for one notations like `^LETTER' stand for
`control-LETTER', and for clarification purposes `\E' can
be used to specify `escape' (the control notation `^['
could lead to misreadings when a left bracket follows,
which it does for the standard CSI sequence); finally
three letter octal sequences, as in `\061', are supported.
To specify that a terminal supports 256-colours, and to
define sequences that home the cursor and produce an
audible bell, one might write:

? set termcap='Co#256,home=\E[H,bel=^G'

The following terminal capabilities are or may be
meaningful for the operation of the built-in line editor
or S-nail in general:

am auto_right_margin: boolean which indicates if
the right margin needs special treatment; the
xenl capability is related, for more see
COLUMNS. This capability is only used when
backed by library support.
clear or cl
clear_screen: clear the screen and home
cursor. (Will be simulated via ho plus cd.)
colors or Co
max_colors: numeric capability specifying the
maximum number of colours. Note that S-nail
does not actually care about the terminal
beside that, but always emits ANSI / ISO 6429
escape sequences; also see colour.
cr carriage_return: move to the first column in
the current row. The default built-in
fallback is `\r'.
cub1 or le cursor_left: move the cursor left one space
(non-destructively). The default built-in
fallback is `\b'.
cuf1 or nd cursor_right: move the cursor right one space
(non-destructively). The default built-in
fallback is `\E[C', which is used by most
terminals. Less often occur `\EC' and `\EOC'.
ed or cd clr_eos: clear the screen.
el or ce clr_eol: clear to the end of line. (Will be
simulated via ch plus repetitions of space
characters.)
home or ho cursor_home: home cursor.
hpa or ch column_address: move the cursor (to the given
column parameter) in the current row. (Will
be simulated via cr plus nd.)
rmcup or te / smcup or ti
exit_ca_mode and enter_ca_mode, respectively:
exit and enter the alternative screen ca-mode,
effectively turning S-nail into a fullscreen
application. This must be enabled explicitly
by setting termcap-ca-mode.
smkx or ks / rmkx or ke
keypad_xmit and keypad_local, respectively:
enable and disable the keypad. This is always
enabled if available, because it seems even
keyboards without keypads generate other key
codes for, e.g., cursor keys in that case, and
only if enabled we see the codes that we are
interested in.
xenl or xn eat_newline_glitch: boolean which indicates
whether a newline written in the last column
of an auto_right_margin indicating terminal is
ignored. With it the full terminal width is
available even on autowrap terminals. This
will be inspected even without `,+termcap,'
features.

Many more capabilities which describe key-sequences are
documented for bind.

termcap-ca-mode
[Option] Allow usage of the exit_ca_mode and enter_ca_mode
termcapabilities in order to enter an alternative
exclusive screen, the so-called ca-mode; this usually
requires special configuration of the PAGER, also
dependent on the value of crt. Note this variable will
only be queried once at program startup and can thus only
be specified in resource files or on the command line.

termcap-disable
[Option] Disable any interaction with a terminal control
library. If set only some generic fallback built-ins and
possibly the content of termcap describe the terminal to
S-nail. Note this variable will only be queried once at
program startup and can thus only be specified in resource
files or on the command line.

tls-ca-dir-USER@HOST, tls-ca-dir-HOST, tls-ca-dir,
tls-ca-file-USER@HOST, tls-ca-file-HOST, tls-ca-file
[Option] Directory and file, respectively, for pools of
trusted CA certificates in PEM (Privacy Enhanced Mail)
format, for the purpose of verification of TLS server
certificates. Concurrent use is possible, the file is
loaded once needed first, the directory lookup is
performed anew as a last resort whenever necessary. The
CA certificate pool built into the TLS library can be
disabled via tls-ca-no-defaults, further fine-tuning is
possible via tls-ca-flags. The directory search requires
special filename conventions, please see
SSL_CTX_load_verify_locations(3) and verify(1) (or
c_rehash(1)).

tls-ca-flags-USER@HOST, tls-ca-flags-HOST, tls-ca-flags
[Option] Can be used to fine-tune behaviour of the X509 CA
certificate storage, and the certificate verification that
is used (also see tls-verify). The value is expected to
consist of a comma-separated list of configuration
directives, with any intervening whitespace being ignored.
The directives directly map to flags that can be passed to
X509_STORE_set_flags(3), which are usually defined in a
file openssl/x509_vfy.h, and the availability of which
depends on the used TLS library version: a directive
without mapping is ignored (error log subject to debug).
Directives currently understood (case-insensitively)
include:

no-alt-chains
If the initial chain is not trusted, do not
attempt to build an alternative chain.
Setting this flag will make OpenSSL
certificate verification match that of older
OpenSSL versions, before automatic building
and checking of alternative chains has been
implemented; also see trusted-first.
no-check-time
Do not check certificate/CRL validity against
current time.
partial-chain
By default partial, incomplete chains which
cannot be verified up to the chain top, a
self-signed root certificate, will not
verify. With this flag set, a chain succeeds
to verify if at least one signing certificate
of the chain is in any of the configured
trusted stores of CA certificates. The
OpenSSL manual page
SSL_CTX_load_verify_locations(3) gives some
advise how to manage your own trusted store
of CA certificates.
strict Disable workarounds for broken certificates.
trusted-first
Try building a chain using issuers in the
trusted store first to avoid problems with
server-sent legacy intermediate certificates.
Newer versions of OpenSSL support alternative
chain checking and enable it by default,
resulting in the same behaviour; also see
no-alt-chains.

tls-ca-no-defaults-USER@HOST, tls-ca-no-defaults-HOST,
tls-ca-no-defaults
(Boolean)[Option] Do not load the default CA locations
that are built into the used to TLS library to verify TLS
server certificates.

tls-config-file
[Option] If this variable is set CONF_modules_load_file(3)
(if announced via `,+modules-load-file,' in tls-features)
is used to allow resource file based configuration of the
TLS library. This happens once the library is used first,
which may also be early during startup (logged with
verbose)! If a non-empty value is given then the given
file, after performing Filename transformations, will be
used instead of the TLS libraries global default, and it
is an error if the file cannot be loaded. The application
name will always be passed as `s-nail'. Some TLS
libraries support application-specific configuration via
resource files loaded like this, please see
tls-config-module.

tls-config-module-USER@HOST, tls-config-module-HOST, tls-config-module
[Option] If file based application-specific configuration
via tls-config-file is available, announced as
`,+ctx-config,' by tls-features, indicating availability
of SSL_CTX_config(3), then, it becomes possible to use a
central TLS configuration file for all programs, including
s-nail, for example

# Register a configuration section for s-nail
s-nail = mailx_master
# The top configuration section creates a relation
# in between dynamic SSL configuration and an actual
# program specific configuration section
[mailx_master]
ssl_conf = mailx_tls_config
# And that program specific configuration section now
# can map diverse tls-config-module names to sections,
# as in: tls-config-module=account_xy
[mailx_tls_config]
account_xy = mailx_account_xy
account_yz = mailx_account_yz
[mailx_account_xy]
MinProtocol = TLSv1.2
Curves=P-521
[mailx_account_yz]
CipherString = TLSv1.2:!aNULL:!eNULL:
MinProtocol = TLSv1.1
Options = Bugs

tls-config-pairs-USER@HOST, tls-config-pairs-HOST, tls-config-pairs
[Option] The value of this variable chain will be
interpreted as a comma-separated list of directive/value
pairs. Directives and values need to be separated by
equals signs `=', any whitespace surrounding pair members
is removed. Keys are (usually) case-insensitive.
Different to when placing these pairs in a
tls-config-module section of a tls-config-file, commas `,'
need to be escaped with a reverse solidus `\' when
included in pairs; also different: if the equals sign `='
is preceded with an asterisk `*' Filename transformations
will be performed on the value; it is an error if these
fail. Unless proper support is announced by tls-features
(`,+conf-ctx,') only the keys below are supported,
otherwise the pairs will be used directly as arguments to
the function SSL_CONF_cmd(3).

Certificate Filename of a TLS client certificate
(chain) required by some servers.
Fallback support via
SSL_CTX_use_certificate_chain_file(3).
Filename transformations are
performed. PrivateKey will be set to
the same value if not initialized
explicitly. Some services support
so-called `external' authentication
if a TLS client certificate was
successfully presented during
connection establishment ("connecting
is authenticating").
CipherString A list of ciphers for TLS
connections, see ciphers(1). By
default no list of ciphers is set,
resulting in a Protocol-specific list
of ciphers (the protocol standards
define lists of acceptable ciphers;
possibly cramped by the used TLS
library). Fallback support via
SSL_CTX_set_cipher_list(3).
Ciphersuites A list of ciphers used for TLSv1.3
connections, see ciphers(1). These
will be joined onto the list of
ciphers from CipherString. Available
if tls-features announces
`,+ctx-set-ciphersuites,', as
necessary via
SSL_CTX_set_ciphersuites(3).
Curves A list of supported elliptic curves,
if applicable. By default no curves
are set. Fallback support via
SSL_CTX_set1_curves_list(3), if
available.
MaxProtocol, MinProtocol
The maximum and minimum supported TLS
versions, respectively. Available if
tls-features announces
`,+ctx-set-maxmin-proto,', as
necessary via
SSL_CTX_set_max_proto_version(3) and
SSL_CTX_set_min_proto_version(3);
these fallbacks use an internal
parser which understands the strings
`SSLv3', `TLSv1', `TLSv1.1',
`TLSv1.2', `TLSv1.3', and the special
value `None', which disables the
given limit.
Options Various flags to set. Fallback via
SSL_CTX_set_options(3), in which case
any other value but (exactly) `Bugs'
results in an error.
PrivateKey Filename of the private key in PEM
format of a TLS client certificate.
If unset, the value of Certificate is
used. Filename transformations are
performed. Fallback via
SSL_CTX_use_PrivateKey_file(3).
Protocol The used TLS protocol. If
tls-features announces `,+conf-ctx,'
or `ctx-set-maxmin-proto' then using
MaxProtocol and MinProtocol is
preferable. Fallback is
SSL_CTX_set_options(3), driven via an
internal parser which understands the
strings `SSLv3', `TLSv1', `TLSv1.1',
`TLSv1.2', `TLSv1.3', and the special
value `ALL'. Multiple protocols may
be given as a comma-separated list,
any whitespace is ignored, an
optional plus sign `+' prefix
enables, a hyphen-minus `-' prefix
disables a protocol, so that `-ALL,
TLSv1.2' enables only the TLSv1.2
protocol.

tls-crl-dir, tls-crl-file
[Option] Specify a directory / a file, respectively, that
contains a CRL in PEM format to use when verifying TLS
server certificates.

tls-features
[Option](Read-only) This expands to a comma-separated list
of the TLS library identity and optional features. To
ease substring matching the string starts and ends with a
comma. Currently supported identities are `libressl'
(LibreSSL) , `libssl-0x30000' (OpenSSL v3.0.0 series),
`libssl-0x10100' (OpenSSL v1.1.x series) and
`libssl-0x10000' (elder OpenSSL series, other clones).
Optional features are preceded with a plus sign `+' when
available, and with a hyphen-minus `-' otherwise.

Currently known features are `conf-ctx'
(tls-config-pairs), `ctx-config' (tls-config-module),
`ctx-set-ciphersuites' (Ciphersuites slot of
tls-config-pairs), `ctx-set-maxmin-proto'
(tls-config-pairs), `modules-load-file' (tls-config-file),
and `tls-rand-file' (tls-rand-file).

tls-fingerprint-USER@HOST, tls-fingerprint-HOST, tls-fingerprint
[Option] It is possible to replace the verification of the
connection peer certificate against the entire local pool
of CAs (for more see Encrypted network communication) with
the comparison against a precalculated certificate message
digest, the so-called fingerprint, to be specified as the
used tls-fingerprint-digest. This fingerprint can for
example be calculated with `tls fingerprint HOST'.

tls-fingerprint-digest-USER@HOST, tls-fingerprint-digest-HOST,
tls-fingerprint-digest
[Option] The message digest to be used when creating TLS
certificate fingerprints, the defaults, if available, in
test order, being `BLAKE2s256', `SHA256'. For the
complete list of digest algorithms refer to
smime-sign-digest.

tls-rand-file
[Option] If tls-features announces `,+tls-rand-file,' then
this will be queried to find a file with random entropy
data which can be used to seed the
P(seudo)R(andom)N(umber)G(enerator), see
RAND_load_file(3). The default filename
(RAND_file_name(3), normally ~/.rnd) will be used if this
variable is not set or empty, or if the Filename
transformations fail. Shall seeding the PRNG have been
successful, RAND_write_file(3) will be called to update
the entropy. Remarks: libraries which do not announce
this feature seed the PRNG by other means.

tls-verify-USER@HOST, tls-verify-HOST, tls-verify
[Option] Variable chain that sets the action to be
performed if an error occurs during TLS server certificate
validation against the specified or default trust stores
tls-ca-dir, tls-ca-file, or the TLS library built-in
defaults (unless usage disallowed via tls-ca-no-defaults),
and as fine-tuned via tls-ca-flags. Valid (case-
insensitive) values are `strict' (fail and close
connection immediately), `ask' (ask whether to continue on
standard input), `warn' (show a warning and continue),
`ignore' (do not perform validation). The default is
`ask'.

toplines If defined, gives the number of lines of a message to be
displayed with the command top; if unset, the first five
lines are printed, if set to 0 the variable screen is
inspected. If the value is negative then its absolute
value will be used for unsigned right shifting (see vexpr)
the screen height.

topsqueeze (Boolean) If set then the top command series will strip
adjacent empty lines and quotations.

ttycharset The character set of the terminal S-nail operates on, and
the one and only supported character set that S-nail can
use if no character set conversion capabilities have been
compiled into it, in which case it defaults to ISO-8859-1.
Otherwise it defaults to UTF-8. Sufficient locale support
provided the default will be preferably deduced from the
locale environment if that is set (for example LC_CTYPE,
see there for more); runtime locale changes will be
reflected by ttycharset except during the program startup
phase and if -S had been used to freeze the given value.
Refer to the section Character sets for the complete
picture about character sets.

typescript-mode
(Boolean) A special multiplex variable that disables all
variables and settings which result in behaviour that
interferes with running S-nail in script(1); it sets
colour-disable, line-editor-disable and (before startup
completed only) termcap-disable. Unsetting it does not
restore the former state of the covered settings.

umask For a safe-by-default policy the process file mode
creation mask umask(2) will be set to `0077' on program
startup after the resource files have been loaded, and
unless this variable is set. By assigning this an empty
value the active setting will not be changed, otherwise
the given value will be made the new file mode creation
mask. Child processes inherit the file mode creation mask
of their parent.

user-HOST, user
[v15-compat] Variable chain that sets a global fallback
user name, used in case none has been given in the
protocol and account-specific URL. This variable defaults
to the name of the user who runs S-nail.

v15-compat Enable upward compatibility with S-nail version 15.0 in
respect to which configuration options are available and
how they are handled. If set to a non-empty value the
command modifier wysh is implied and thus enforces Shell-
style argument quoting over Old-style argument quoting for
all commands which support both. This manual uses
[v15-compat] and [no v15-compat] to refer to the new and
the old way of doing things, respectively.

verbose Verbose mode enables logging of informational context
messages. Historically a (Boolean) variable, this can
either be set multiple times (what the command line option
-v uses), or be assigned a numeric value in order to
increase verbosity. Assigning the value 0 disables
verbosity and thus (almost) equals unset. The maximum
number is 3. Also see debug.

version, version-date, version-hexnum, version-major, version-minor,
version-update
(Read-only) S-nail version information: the first variable
is a string with the complete version identification, the
second the release date in ISO 8601 notation without time.
The third is a 32-bit hexadecimal number with the upper 8
bits storing the major, followed by the minor and update
version numbers which occupy 12 bits each. The latter
three variables contain only decimal digits: the major,
minor and update version numbers. The output of the
command version will include this information.

writebackedited
If this variable is set messages modified using the edit
or visual commands are written back to the current folder
when it is quit; it is only honoured for writable folders
in MBOX format, though. Note that the editor will be
pointed to the raw message content in that case, i.e.,
neither MIME decoding nor decryption will have been
performed, and proper mbox-rfc4155 `From_' quoting of
newly added or edited content is also left as an exercise
to the user.

ENVIRONMENT

The term "environment variable" should be considered an indication that
these variables are either standardized as vivid parts of process
environments, or that they are commonly found in there. The process
environment is inherited from the sh(1) once S-nail is started, and
unless otherwise explicitly noted handling of the following variables
transparently integrates into that of the INTERNAL VARIABLES from S-
nail's point of view. This means they can be managed via set and
unset, causing automatic program environment updates (to be inherited
by newly created child processes).

In order to integrate other environment variables equally they need to
be imported (linked) with the command environ. This command can also
be used to set and unset non-integrated environment variables from
scratch, sufficient system support provided. The following example,
applicable to a POSIX shell, sets the COLUMNS environment variable for
S-nail only, and beforehand exports the EDITOR in order to affect any
further processing in the running shell:

$ EDITOR="vim -u ${HOME}/.vimrc"
$ export EDITOR
$ COLUMNS=80 s-nail -R

COLUMNS The user's preferred width in column positions for the
terminal screen. Queried and used once on program startup
in interactive or batch (-#) mode, actively managed for
child processes and the MLE (see On terminal control and
line editor) in interactive mode thereafter. Non-
interactive mode always uses, and the fallback default is
a compile-time constant, by default 80 columns. If in
batch mode COLUMNS and LINES are both set but not both are
usable (empty, not a number, or 0) at program startup,
then the real terminal screen size will be (tried to be)
determined once. (Normally the sh(1) manages these
variables, and unsets them for pipe specifications etc.)

DEAD The name of the (mailbox) folder to use for saving aborted
messages if save is set; this defaults to ~/:dead.letter.
If the variable debug is set no output will be generated,
otherwise the contents of the file will be replaced.
Except shell globs Filename transformations (also see
folder) will be performed.

EDITOR Pathname of the text editor to use for the edit command
and ~e (see COMMAND ESCAPES); VISUAL is used for a more
display oriented editor.

HOME The user's home directory. This variable is only used
when it resides in the process environment. The calling
user's home directory will be used instead if this
directory does not exist, is not accessible or cannot be
read; it will always be used for the root user. (No test
for being writable is performed to allow usage by non-
privileged users within read-only jails, but dependent on
settings this directory is a default write target for, for
example, DEAD, MBOX and more.)

LC_ALL, LC_CTYPE, LANG
[Option] The (names in lookup order of the) locale(7) (and
/ or see setlocale(3)) which indicates the used Character
sets. Runtime changes trigger automatic updates of the
entire locale system, which includes updating ttycharset
(except during startup if the variable has been frozen via
-S).

LINES The user's preferred number of lines for the terminal
screen. The behaviour is as described for COLUMNS, yet
the compile-time constant used in non-interactive mode and
as a fallback defaults to 24 (lines).

LISTER Pathname of the directory lister to use in the folders
command when operating on local mailboxes. Default is
ls(1) (path search through SHELL).

LOGNAME Upon startup S-nail will actively ensure that this
variable refers to the name of the user who runs S-nail,
in order to be able to pass a verified name to any newly
created child process.

MAIL Is used as the user's primary system mailbox unless inbox
is set. If the environmental fallback is also not set, a
built-in compile-time default is used. This is assumed to
be an absolute pathname.

MAILCAPS [Option] Override the default path search of The Mailcap
files: any existing file therein will be loaded in
sequence, appending any content to the list of MIME type
handler directives. The RFC 1524 standard imposed default
value is assigned otherwise: `~/.mailcap:/etc/mailcap:
/usr/etc/mailcap:/usr/local/etc/mailcap'. (The default
value is a compile-time [Option].)

MAILRC Is used as a startup file instead of ~/:.mailrc if set.
In order to avoid side-effects from configuration files
scripts should either set this variable to /dev/null or
the -: command line option should be used.

MAILX_NO_SYSTEM_RC
If this variable is set then reading of s-nail.rc (aka
system-mailrc) at startup is inhibited, i.e., the same
effect is achieved as if S-nail had been started up with
the option -: (and according argument) or -n. This
variable is only used when it resides in the process
environment.

MBOX The name of the user's secondary mailbox file. A logical
subset of the special Filename transformations (also see
folder) are supported. The default is ~/:mbox.
Traditionally this MBOX is used as the file to save
messages from the primary system mailbox that have been
read. Also see Message states.

NETRC [v15-compat][Option] This variable overrides the default
location of the user's ~/:.netrc file.

PAGER Pathname of the program to use for backing the command
more, and when the crt variable enforces usage of a pager
for output. The default paginator is more(1) (path search
through SHELL).

S-nail inspects the contents of this variable: if its
contains the string "less" then a non-existing environment
variable LESS will be set to (the portable) `RI', likewise
for "lv" LV will optionally be set to `-c'. Also see
colour-pager.

PATH A colon-separated list of directories that is searched by
the shell when looking for commands, for example
`/bin:/usr/bin:/usr/local/bin'.

POSIXLY_CORRECT
This environment entry is automatically squared with
posix.

SHELL The shell to use for the commands !, shell, the ~! COMMAND
ESCAPES and when starting subprocesses. A default shell
is used if this environment variable is not defined.

SOCKS5_PROXY
This environment entry is automatically squared with
socks-proxy.

SOURCE_DATE_EPOCH
Specifies a time in seconds since the Unix epoch
(1970-01-01) to be used in place of the current time.
This variable is looked up upon program startup, and its
existence will switch S-nail to a reproducible mode
(https://reproducible-builds.org) which uses deterministic
random numbers, a special fixated pseudo LOGNAME and more.
This operation mode is used for development and by
software packagers. [v15 behaviour may differ] Currently
an invalid setting is only ignored, rather than causing a
program abortion.

$ SOURCE_DATE_EPOCH=`date +%s` s-nail

TERM [Option] The terminal type for which output is to be
prepared. For extended colour and font control please
refer to Coloured display, and for terminal management in
general to On terminal control and line editor.

TMPDIR Except for the root user this variable defines the
directory for temporary files to be used instead of /:tmp
(or the given compile-time constant) if set, existent,
accessible as well as read- and writable. This variable
is only used when it resides in the process environment,
but S-nail will ensure at startup that this environment
variable is updated to contain a usable temporary
directory.

USER Identical to LOGNAME (see there), but this variable is not
standardized, should therefore not be used, and is only
corrected if already set.

VISUAL Pathname of the text editor to use for the visual command
and ~v (see COMMAND ESCAPES); EDITOR is used for a less
display oriented editor.

FILES

~/.mailcap, /etc/mailcap
[Option] Personal and system-wide MIME type handler
definition files, see The Mailcap files. (The shown names
are part of the RFC 1524 standard search path MAILCAPS.)

~/:.mailrc, s-nail.rc
User-specific and system-wide files giving initial
commands, the Resource files. (The used filenames come
from MAILRC and system-mailrc, respectively.)

~/:mbox The default value for MBOX.

~/:.mime.types, /:etc/:mime.types
Personal and system-wide MIME types, see The mime.types
files.

~/:.netrc [v15-compat][Option] The default location of the user's
.netrc file - the section The .netrc file documents the
file format. The used path can be set via NETRC.

/dev/null The data sink null(4).

~/.rnd [Option] Possible location for persistent random entropy
seed storage, see tls-rand-file.

Resource files

Upon startup S-nail reads in several resource files, in order:

s-nail.rc System wide initialization file (system-mailrc). Reading
of this file can be suppressed, either by using the -:
(and according argument) or -n command line options, or by
setting the ENVIRONMENT variable MAILX_NO_SYSTEM_RC.

~/:.mailrc File giving initial commands. A different file can be
chosen by setting the ENVIRONMENT variable MAILRC.
Reading of this file can be suppressed with the -: command
line option.

mailx-extra-rc
Defines a startup file to be read after all other resource
files. It can be used to specify settings that are not
understood by other mailx(1) implementations, for example.

The content of these files is interpreted as follows:

+o The whitespace characters space, tabulator and newline, as well as
those defined by the variable ifs, are removed from the beginning
and end of input lines.
+o Empty lines are ignored.
+o Any other line is interpreted as a command. It may be spread over
multiple input lines if the newline character is "escaped" by
placing a reverse solidus character `\' as the last character of
the line; whereas any leading whitespace of follow lines is
ignored, trailing whitespace before a escaped newline remains in
the input.
+o If the line (content) starts with the number sign `#' then it is a
comment-command and also ignored. (The comment-command is a real
command, which does nothing, and therefore the usual follow lines
mechanism applies!)

Errors while loading these files are subject to the settings of errexit
and posix. More files with syntactically equal content can be
sourceed. The following, saved in a file, would be an examplary
content:

# This line is a comment command. And y\
es, it is really continued here.
set debug \
verbose
set editheaders

The mime.types files
As stated in HTML mail and MIME attachments S-nail needs to learn about
MIME (Multipurpose Internet Mail Extensions) media types in order to
classify message and attachment content. One source for them are
mime.types files, the loading of which can be controlled by setting the
variable mimetypes-load-control. Another is the command mimetype,
which also offers access to S-nails MIME type cache. mime.types files
have the following syntax:

type/subtype extension [extension ...]
# For example text/html html htm

where `type/subtype' define the MIME media type, as standardized in RFC
2046: `type' is used to declare the general type of data, while the
`subtype' specifies a specific format for that type of data. One or
multiple filename `extension's, separated by whitespace, can be bound
to the media type format. Comments may be introduced anywhere on a
line with a number sign `#', causing the remaining line to be
discarded. S-nail also supports an extended, non-portable syntax in
especially crafted files, which can be loaded via the alternative value
syntax of mimetypes-load-control, and prepends an optional
`type-marker':

[type-marker ]type/subtype extension [extension ...]

The following type markers are supported:

? Treat message parts with this content as plain text.
?t The same as plain ?.
?h Treat message parts with this content as HTML tagsoup. If
the [Option]al HTML-tagsoup-to-text converter is not
available treat the content as plain text instead.
?H Likewise ?h, but instead of falling back to plain text
require an explicit content handler to be defined.
?q If no handler can be found a text message is displayed
which says so. This can be annoying, for example
signatures serve a contextual purpose, their content is of
no use by itself. This marker will avoid displaying the
text message.

Further reading: for sending messages: mimetype,
mime-allow-text-controls, mimetypes-load-control. For reading etc.
messages: HTML mail and MIME attachments, The Mailcap files, mimetype,
mime-counter-evidence, mimetypes-load-control, pipe-TYPE/SUBTYPE,
pipe-EXTENSION.

The Mailcap files

[Option] RFC 1524 defines a "User Agent Configuration Mechanism" to be
used to inform mail user agent programs about the locally installed
facilities for handling various data formats, i.e., about commands and
how they can be used to display, edit et cetera MIME part contents, as
well as a default path search that includes multiple possible locations
of resource files, and the MAILCAPS environment variable to overwrite
that. Handlers found from doing the path search will be cached, the
command mailcap operates on that cache, and the variable
mailcap-disable will suppress automatic loading, and usage of any
mailcap handlers. HTML mail and MIME attachments gives a general
overview of how MIME types are handled.

"Mailcap" files consist of a set of newline separated entries. Comment
lines start with a number sign `#' (in the first column!) and are
ignored. Empty lines are ignored. All other lines are interpreted as
mailcap entries. An entry definition may be split over multiple lines
by placing the reverse solidus character `\' last in all but the final
line. The standard does not specify how leading whitespace of
successive lines is to be treated, therefore they are retained.

"Mailcap" entries consist of a number of semicolon `;' separated
fields. The first two fields are mandatory and must occur in the
specified order, the remaining fields are optional and may appear in
any order. Leading and trailing whitespace of field content is ignored
(removed). The reverse solidus `\' character can be used to escape any
following character including semicolon and itself in the content of
the second field, and in value parts of any optional key/value field.

The first field defines the MIME `TYPE/SUBTYPE' the entry is about to
handle (case-insensitively). If the subtype is specified as an
asterisk `*' the entry is meant to match all subtypes of the named
type, e.g., `audio/*' would match any audio type. The second field is
the view shell command used to display MIME parts of the given type.

Data consuming shell commands will be fed message (MIME part) data on
standard input unless one or more instances of the (unquoted) string
`%s' are used: these formats will be replaced with a temporary
file(name) that has been prefilled with the parts data. Data producing
shell commands are expected to generata data on their standard output
unless that format is used. In all cases any given `%s' format is
replaced with a properly shell quoted filename. When a command
requests a temporary file via `%s' then that will be removed again, as
if the x-mailx-tmpfile and x-mailx-tmpfile-fill flags had been set;
unless the command requests x-mailx-async the x-mailx-tmpfile-unlink
flag is also implied; see below for more.

Optional fields define single-word flags (case-insensitive), or key /
value pairs consisting of a case-insensitive keyword, an equals sign
`=', and a shell command; whitespace surrounding the equals sign is
removed. Optional fields include the following:

compose A program that can be used to compose a new body or body
part in the given format. (Currently unused.)

composetyped
Similar to the compose field, but is to be used when the
composing program needs to specify the `Content-type:'
header field to be applied to the composed data.
(Currently unused.)

copiousoutput
A flag field which indicates that the output of the view
command is integrable into S-nails normal visual display.
It is mutually exclusive with needsterminal.

description A textual description that describes this type of data.
The text may optionally be enclosed within double
quotation marks `"'.

edit A program that can be used to edit a body or body part in
the given format. (Currently unused.)

nametemplate
This field specifies a filename format for the `%s' format
used in the shell command fields, in which `%s' will be
replaced by a random string. (The filename is also stored
in and passed to subprocesses via
MAILX_FILENAME_TEMPORARY.) The standard says this is "only
expected to be relevant in environments where filename
extensions are meaningful", and so this field is ignored
unless the `%s' is a prefix, optionally followed by
(ASCII) alphabetic and numeric characters, the underscore
and the period. For example, to specify that a JPG file
is to be passed to an image viewer with a name ending in
`.jpg', `nametemplate=%s.jpg' can be used.

needsterminal
This flag field indicates that the given shell command
must be run on an interactive terminal. S-nail will
temporarily release the terminal to the given command in
interactive mode, in non-interactive mode this entry will
be entirely ignored; this flag implies x-mailx-noquote.

print A program that can be used to print a message or body part
in the given format. (Currently unused.)

test Specifies a program to be run to test some condition, for
example, the machine architecture, or the window system in
use, to determine whether or not this mailcap entry
applies. If the test fails, a subsequent mailcap entry
should be sought; also see x-mailx-test-once. Standard
I/O of the test program is redirected from and to
/dev/null, and the format `%s' is not supported (the data
does not yet exist).

textualnewlines
A flag field which indicates that this type of data is
line-oriented and that, if encoded in `base64', all
newlines should be converted to canonical form (CRLF)
before encoding, and will be in that form after decoding.
(Currently unused.)

x11-bitmap Names a file, in X11 bitmap (xbm) format, which points to
an appropriate icon to be used to visually denote the
presence of this kind of data. This field is not used by
S-nail.

x-mailx-async
Extension flag field that denotes that the given view
command shall be executed asynchronously, without blocking
S-nail. Cannot be used in conjunction with needsterminal;
the standard output of the command will go to /dev/null.

x-mailx-noquote
An extension flag field that indicates that even a
copiousoutput view command shall not be used when quoteing
messages, as it would by default.

x-mailx-test-once
Extension flag which denotes whether the given test
command shall be evaluated once only with its exit status
being cached. This is handy if some global unchanging
condition is to be queried, like "running under the X
Window System".

x-mailx-tmpfile
Extension flag field that requests creation of a zero-
sized temporary file, the name of which is to be placed in
the environment variable MAILX_FILENAME_TEMPORARY. It is
an error to use this flag with commands that include a
`%s' format (because that is implemented by means of this
temporary file).

x-mailx-tmpfile-fill
Normally the MIME part content is passed to the handler
via standard input; if this flag is set then the data will
instead be written into the implied x-mailx-tmpfile. In
order to cause deletion of the temporary file you will
have to set x-mailx-tmpfile-unlink explicitly! It is an
error to use this flag with commands that include a `%s'
format.

x-mailx-tmpfile-unlink
Extension flag field that requests that the temporary file
shall be deleted automatically when the command loop is
entered again at latest. It is an error to use this flag
with commands that include a `%s' format, or in
conjunction with x-mailx-async. x-mailx-tmpfile is
implied.

x-mailx-last-resort
An extension flag that indicates that this handler shall
only be used as a last resort, when no other source (see
HTML mail and MIME attachments) provides a MIME handler.

x-mailx-ignore
An extension that enforces that this handler is not used
at all.

The standard includes the possibility to define any number of
additional fields, prefixed by `x-'. Flag fields apply to the entire
"Mailcap" entry -- in some unusual cases, this may not be desirable,
but differentiation can be accomplished via separate entries, taking
advantage of the fact that subsequent entries are searched if an
earlier one does not provide enough information. For example, if a
view command needs to specify the needsterminal flag, but the compose
command shall not, the following will help out the latter:

application/postscript; ps-to-terminal %s; needsterminal
application/postscript; ps-to-terminal %s; compose=idraw %s

In value parts of command fields any occurrence of the format string
`%t' will be replaced by the `TYPE/SUBTYPE' specification. Any named
parameter from a messages' `Content-type:' field may be embedded into
the command line using the format `%{' followed by the parameter name
and a closing brace `}' character. The entire parameter should appear
as a single command line argument, regardless of embedded spaces, shell
quoting will be performed by the RFC 1524 processor, thus:

# Message
Content-type: multipart/mixed; boundary=42

# Mailcap file
multipart/*; /usr/local/bin/showmulti \
%t %{boundary} ; composetyped = /usr/local/bin/makemulti

# Executed shell command
/usr/local/bin/showmulti multipart/mixed 42

Note that S-nail does not support handlers for multipart MIME parts as
shown in this example (as of today). It does not support the
additional formats `%n' and `%F'. An example file, also showing how to
properly deal with the expansion of `%s', which includes any quotes
that are necessary to make it a valid shell argument by itself and thus
will cause undesired behaviour when placed in additional user-provided
quotes:

# Comment line
text/richtext; richtext %s; copiousoutput

text/x-perl; perl -cWT %s; nametemplate = %s.pl

# Exit EX_TEMPFAIL=75 on signal
application/pdf; \
infile=%s\; \
trap "rm -f ${infile}" EXIT\; \
trap "exit 75" INT QUIT TERM\; \
mupdf "${infile}"; \
test = [ -n "${DISPLAY}" ]; \
nametemplate = %s.pdf; x-mailx-async
application/pdf; pdftotext -layout - -; copiousoutput

application/*; echo "This is \\"%t\\" but \
is 50 \% Greek to me" \; < %s head -c 512 | cat -vet; \
copiousoutput; x-mailx-noquote; x-mailx-last-resort

Further reading: HTML mail and MIME attachments, The mime.types files,
mimetype, MAILCAPS, mime-counter-evidence, pipe-TYPE/SUBTYPE,
pipe-EXTENSION.

The .netrc file
User credentials for machine accounts (see On URL syntax and credential
lookup) can be placed in the .netrc file, which will be loaded and
cached when requested by netrc-lookup. The default location ~/:.netrc
may be overridden by the NETRC environment variable. As long as syntax
constraints are honoured the file source may be replaced with the
output of the shell command set in netrc-pipe, to load an encrypted
file, for example. The cache can be managed with the command netrc.

The file consists of space, tabulator or newline separated tokens.
This parser implements a superset of the original BSD syntax, but users
should nonetheless be aware of portability glitches, shall their .netrc
be usable across multiple programs and platforms:

+o BSD only supports double quotation marks, for example `password
"pass with spaces"'.
+o BSD (only?) supports escaping of single characters via a reverse
solidus (a space could be escaped via `\ '), in- as well as outside
of a quoted string. This method is assumed to be present, and will
actively be used to quote double quotation marks `"' and reverse
solidus `\' characters inside the login and password tokens, for
example for display purposes.
+o BSD does not require a final quotation mark of the last user input
token.
+o The original BSD (Berknet) parser also supported a format which
allowed tokens to be separated with commas - whereas at least
Hewlett-Packard still seems to support this syntax, this parser
does not!
+o As a non-portable extension some widely-used programs support
shell-style comments: if an input line starts, after any amount of
whitespace, with a number sign `#', then the rest of the line is
ignored.
+o Whereas other programs may require that the .netrc file is
accessible by only the user if it contains a password token for any
other login than "anonymous", this parser will always require these
strict permissions.

Of the following list of supported tokens this parser uses (and caches)
machine, login and password. An existing default entry will not be
used.

machine name
The hostname of the entries' machine, lowercase-normalized
before use. Any further file content, until either end-
of-file or the occurrence of another machine or a default
first-class token is bound (only related) to the machine
name.

As an extension that should not be the cause of any
worries this parser supports a single wildcard prefix for
name:

machine *.example.com login USER password PASS
machine pop3.example.com login USER password PASS
machine smtp.example.com login USER password PASS

which would match `xy.example.com' as well as
`pop3.example.com', but neither `example.com' nor
`local.smtp.example.com'. In the example neither
`pop3.example.com' nor `smtp.example.com' will be matched
by the wildcard, since the exact matches take precedence
(it is however faster to specify it the other way around).

default This is the same as machine except that it is a fallback
entry that is used shall none of the specified machines
match; only one default token may be specified, and it
must be the last first-class token.

login name The user name on the remote machine.

password string
The user's password on the remote machine.

account string
Supply an additional account password. This is merely for
FTP purposes.

macdef name Define a macro. A macro is defined with the specified
name; it is formed from all lines beginning with the next
line and continuing until a blank line is (consecutive
newline characters are) encountered. (Note that macdef
entries cannot be utilized by multiple machines, too, but
must be defined following the machine they are intended to
be used with.) If a macro named init exists, it is
automatically run as the last step of the login process.
This is merely for FTP purposes.

EXAMPLES

An example configuration

# This example assumes v15.0 compatibility mode
set v15-compat

# Request strict TLL transport layer security checks
set tls-verify=strict

# Where are the up-to-date TLS certificates?
# (Since we manage up-to-date ones explicitly, do not use any,
# possibly outdated, default certificates shipped with OpenSSL)
#set tls-ca-dir=/etc/ssl/certs
set tls-ca-file=/etc/ssl/certs/ca-certificates.crt
set tls-ca-no-defaults
#set tls-ca-flags=partial-chain
wysh set smime-ca-file="${tls-ca-file}" \
smime-ca-no-defaults #smime-ca-flags="${tls-ca-flags}"

# This could be outsourced to a central configuration file via
# tls-config-file plus tls-config-module if the used library allows.
# CipherString: explicitly define the list of ciphers, which may
# improve security, especially with protocols older than TLS v1.2.
# See ciphers(1). Possibly best to only use tls-config-pairs-HOST
# (or -USER@HOST), as necessary, again..
# Note that TLSv1.3 uses Ciphersuites= instead, which will join
# with CipherString (if protocols older than v1.3 are allowed)
# Curves: especially with TLSv1.3 curves selection may be desired.
# MinProtocol,MaxProtocol: do not use protocols older than TLS v1.2.
# Change this only when the remote server does not support it:
# maybe use chain support via tls-config-pairs-HOST / -USER@HOST
# to define such explicit exceptions, then, e.g.,
# MinProtocol=TLSv1.1
if "$tls-features" =% ,+ctx-set-maxmin-proto,
wysh set tls-config-pairs='\
CipherString=TLSv1.2:!aNULL:!eNULL:@STRENGTH,\
Curves=P-521:P-384:P-256,\
MinProtocol=TLSv1.1'
else
wysh set tls-config-pairs='\
CipherString=TLSv1.2:!aNULL:!eNULL:@STRENGTH,\
Curves=P-521:P-384:P-256,\
Protocol=-ALL\,+TLSv1.1 \, +TLSv1.2\, +TLSv1.3'
endif

# Essential setting: select allowed character sets
set sendcharsets=utf-8,iso-8859-1

# A very kind option: when replying to a message, first try to
# use the same encoding that the original poster used herself!
set reply-in-same-charset

# When replying, do not merge From: and To: of the original message
# into To:. Instead old From: -> new To:, old To: -> merge Cc:.
set recipients-in-cc

# When sending messages, wait until the Mail-Transfer-Agent finishs.
# Only like this you will be able to see errors reported through the
# exit status of the MTA (including the built-in SMTP one)!
set sendwait

# Only use built-in MIME types, no mime.types(5) files
set mimetypes-load-control

# Default directory where we act in (relative to $HOME)
set folder=mail
# A leading "+" (often) means: under *folder*
# *record* is used to save copies of sent messages
set MBOX=+mbox.mbox DEAD=+dead.txt \
record=+sent.mbox record-files record-resent

# Make "file mymbox" and "file myrec" go to..
shortcut mymbox %:+mbox.mbox myrec +sent.mbox

# Not really optional, e.g., for S/MIME
set from='Your Name <address@exam.ple>'

# It may be necessary to set hostname and/or smtp-hostname
# if the "SERVER" of mta and "domain" of from do not match.
# The `urlencode' command can be used to encode USER and PASS
set mta=(smtps?|submissions?)://[USER[:PASS]@]SERVER[:PORT] \
smtp-auth=login/plain... \
smtp-use-starttls

# Never refuse to start into interactive mode, and more
set emptystart \
colour-pager crt= \
followup-to followup-to-honour=ask-yes fullnames \
history-file=+.s-nailhist history-size=-1 history-gabby \
mime-counter-evidence=0b1111 \
prompt='?\$?!\$!/\$^ERRNAME[\$account#\$mailbox-display]? ' \
reply-to-honour=ask-yes \
umask=

# Only include the selected header fields when typing messages
headerpick type retain from_ date from to cc subject \
message-id mail-followup-to reply-to
# ...when forwarding messages
headerpick forward retain subject date from to cc
# ...when saving message, etc.
#headerpick save ignore ^Original-.*$ ^X-.*$

# Some mailing lists
mlist '@xyz-editor\.xyz$' '@xyzf\.xyz$'
mlsubscribe '^xfans@xfans\.xyz$'

# Handle a few file extensions (to store MBOX databases)
filetype bz2 'bzip2 -dc' 'bzip2 -zc' \
gz 'gzip -dc' 'gzip -c' xz 'xz -dc' 'xz -zc' \
zst 'zstd -dc' 'zstd -19 -zc' \
zst.pgp 'gpg -d | zstd -dc' 'zstd -19 -zc | gpg -e'

# A real life example of a very huge free mail provider
# Instead of directly placing content inside `account',
# we `define' a macro: like that we can switch "accounts"
# from within *on-compose-splice*, for example!
define XooglX {
set folder=~/spool/XooglX inbox=+syste.mbox sent=+sent
set from='Your Name <address@examp.ple>'

set pop3-no-apop-pop.gmXil.com
shortcut pop %:pop3s://pop.gmXil.com
shortcut imap %:imaps://imap.gmXil.com
# Or, entirely IMAP based setup
#set folder=imaps://imap.gmail.com record="+[Gmail]/Sent Mail" \
# imap-cache=~/spool/cache

set mta=smtp://USER:PASS@smtp.gmXil.com smtp-use-starttls
# Alternatively:
set mta=smtps://USER:PASS@smtp.gmail.com:465
}
account XooglX {
\call XooglX
}

# Here is a pretty large one which does not allow sending mails
# if there is a domain name mismatch on the SMTP protocol level,
# which would bite us if the value of from does not match, e.g.,
# for people who have a sXXXXeforge project and want to speak
# with the mailing list under their project account (in from),
# still sending the message through their normal mail provider
define XandeX {
set folder=~/spool/XandeX inbox=+syste.mbox sent=+sent
set from='Your Name <address@exam.ple>'

shortcut pop %:pop3s://pop.yaXXex.com
shortcut imap %:imaps://imap.yaXXex.com

set mta=smtps://USER:PASS@smtp.yaXXex.com:465 \
hostname=yaXXex.com smtp-hostname=
}
account XandeX {
\call Xandex
}

# Create some new commands so that, e.g., `ls /tmp' will..
commandalias lls '!ls ${LS_COLOUR_FLAG} -aFlrS'
commandalias llS '!ls ${LS_COLOUR_FLAG} -aFlS'

set pipe-message/external-body='?* echo $MAILX_EXTERNAL_BODY_URL'

# We do not support gpg(1) directly yet. But simple --clearsign'd
# message parts can be dealt with as follows:
define V {
localopts yes
wysh set pipe-text/plain=$'?*#++=?\
< "${MAILX_FILENAME_TEMPORARY}" awk \
-v TMPFILE="${MAILX_FILENAME_TEMPORARY}" \'\
BEGIN{done=0}\
/^-----BEGIN PGP SIGNED MESSAGE-----/,/^$/ {\
if(done++ != 0)\
next;\
print "--- GPG --verify ---";\
system("gpg --verify " TMPFILE " 2>&1");\
print "--- GPG --verify ---";\
print "";\
next;\
}\
/^-----BEGIN PGP SIGNATURE-----/,\
/^-----END PGP SIGNATURE-----/{\
next;\
}\
{print}\
\''
print
}
commandalias V '\'call V

When storing passwords in ~/:.mailrc appropriate permissions should be
set on this file with `$ chmod 0600 ~/:.mailrc'. If the [Option]al
netrc-lookup is available user credentials can be stored in the central
~/:.netrc file instead; e.g., here is a different version of the
example account that sets up SMTP and POP3:

define XandeX {
set folder=~/spool/XandeX inbox=+syste.mbox sent=+sent
set from='Your Name <address@exam.ple>'
set netrc-lookup
# Load an encrypted ~/.netrc by uncommenting the next line
#set netrc-pipe='gpg -qd ~/.netrc.pgp'

set mta=smtps://smtp.yXXXXx.ru:465 \
smtp-hostname= hostname=yXXXXx.com
set pop3-keepalive=240 pop3-no-apop-pop.yXXXXx.ru
commandalias xp fi pop3s://pop.yXXXXx.ru
}
account XandeX {
\call XandeX
}

and, in the ~/:.netrc file:

machine *.yXXXXx.ru login USER password PASS

This configuration should now work just fine:

$ echo text | s-nail -dvv -AXandeX -s Subject user@exam.ple

S/MIME step by step
[Option] The first thing that is needed for Signed and encrypted
messages with S/MIME is a personal certificate, and a private key. The
certificate contains public information, in particular a name and email
address(es), and the public key that can be used by others to encrypt
messages for the certificate holder (the owner of the private key), and
to verify signed messages generated with that certificate('s private
key). Whereas the certificate is included in each signed message, the
private key must be kept secret. It is used to decrypt messages that
were previously encrypted with the public key, and to sign messages.

For personal use it is recommended to get a S/MIME certificate from one
of the major CAs on the Internet. Many CAs offer such certificates for
free. Usually offered is a combined certificate and private key in
PKCS#12 format which S-nail does not accept directly. To convert it to
PEM format, the following shell command can be used; please read on for
how to use these PEM files.

$ openssl pkcs12 -in cert.p12 -out certpem.pem -clcerts -nodes
$ # Alternatively
$ openssl pkcs12 -in cert.p12 -out cert.pem -clcerts -nokeys
$ openssl pkcs12 -in cert.p12 -out key.pem -nocerts -nodes

There is also https://www.CAcert.org which issues client and server
certificates to members of their community for free; their root
certificate (https://www.cacert.org/certs/root.crt) is often not in the
default set of trusted CA root certificates, though, which means their
root certificate has to be downloaded separately, and needs to be part
of the S/MIME certificate validation chain by including it in
smime-ca-dir or as a vivid member of the smime-ca-file. But let us
take a step-by-step tour on how to setup S/MIME with a certificate from
CAcert.org despite this situation!

First of all you will have to become a member of the CAcert.org
community, simply by registrating yourself via the web interface. Once
you are, create and verify all email addresses you want to be able to
create signed and encrypted messages for/with using the corresponding
entries of the web interface. Now ready to create S/MIME certificates,
so let us create a new "client certificate", ensure to include all
email addresses that should be covered by the certificate in the
following web form, and also to use your name as the "common name".

Create a private key and a certificate request on your local computer
(please see the manual pages of the used commands for more in-depth
knowledge on what the used arguments etc. do):

$ openssl req -nodes -newkey rsa:4096 -keyout key.pem -out
creq.pem

Afterwards copy-and-paste the content of "creq.pem" into the
certificate-request (CSR) field of the web form on the CAcert.org
website (you may need to unfold some "advanced options" to see the
corresponding text field). This last step will ensure that your
private key (which never left your box) and the certificate belong
together (through the public key that will find its way into the
certificate via the certificate-request). You are now ready and can
create your CAcert certified certificate. Download and store or copy-
and-paste it as "pub.crt".

Yay. In order to use your new S/MIME setup a combined private
key/public key (certificate) file has to be created:

$ cat key.pem pub.crt > ME@HERE.com.paired

This is the file S-nail will work with. If you have created your
private key with a passphrase then S-nail will ask you for it whenever
a message is signed or decrypted, unless this operation has been
automated as described in Signed and encrypted messages with S/MIME.
Set the following variables to henceforth use S/MIME (setting
smime-ca-file is of interest for verification only):

? set smime-ca-file=ALL-TRUSTED-ROOT-CERTS-HERE \
smime-sign-cert=ME@HERE.com.paired \
smime-sign-digest=SHA512 \
smime-sign from=myname@my.host

Using CRLs with S/MIME or TLS
[Option] Certification authorities (CAs) issue certificate revocation
lists (CRLs) on a regular basis. These lists contain the serial
numbers of certificates that have been declared invalid after they have
been issued. Such usually happens because the private key for the
certificate has been compromised, because the owner of the certificate
has left the organization that is mentioned in the certificate, etc.
To seriously use S/MIME or TLS verification, an up-to-date CRL is
required for each trusted CA. There is otherwise no method to
distinguish between valid and invalidated certificates. S-nail
currently offers no mechanism to fetch CRLs, nor to access them on the
Internet, so they have to be retrieved by some external mechanism.

S-nail accepts CRLs in PEM format only; CRLs in DER format must be
converted, like, e.g.:

$ openssl crl -inform DER -in crl.der -out crl.pem

To tell S-nail about the CRLs, a directory that contains all CRL files
(and no other files) must be created. The smime-crl-dir or tls-crl-dir
variables, respectively, must then be set to point to that directory.
After that, S-nail requires a CRL to be present for each CA that is
used to verify a certificate.

FAQ

In general it is a good idea to turn on debug (-d) and / or verbose
(-v, twice) if something does not work well. Very often a diagnostic
message can be produced that leads to the problems' solution.

S-nail shortly hangs on startup
This can have two reasons, one is the necessity to wait for a file lock
and cannot be helped, the other being that S-nail calls the function
uname(2) in order to query the nodename of the box (sometimes the real
one is needed instead of the one represented by the internal variable
hostname). One may have varying success by ensuring that the real
hostname and `localhost' have entries in /etc/hosts, or, more
generally, that the name service is properly setup - and does
hostname(1) return the expected value? Does this local hostname have a
domain suffix? RFC 6762 standardized the link-local top-level domain
`.local', try again after adding an (additional) entry with this
extension.

I cannot login to Google mail (via OAuth)
Since 2014 some free service providers classify programs as "less
secure" unless they use a special authentication method (OAuth 2.0)
which was not standardized for non-HTTP protocol authentication token
query until August 2015 (RFC 7628).

Different to Kerberos / GSSAPI, which is developed since the mid of the
1980s, where a user can easily create a local authentication ticket for
her- and himself with the locally installed kinit(1) program, that
protocol has no such local part but instead requires a world-wide-web
query to create or fetch a token; since there is no local cache this
query would have to be performed whenever S-nail is invoked (in
interactive sessions situation may differ).

S-nail does not directly support OAuth. It, however, supports XOAUTH2
/ OAUTHBEARER, see But, how about XOAUTH2 / OAUTHBEARER? If that is not
used it is necessary to declare S-nail a "less secure app" (on the
providers account web page) in order to read and send mail. However,
it also seems possible to take the following steps instead:

1. give the provider the number of a mobile phone,
2. enable "2-Step Verification",
3. create an application specific password (16 characters), and
4. use that special password instead of the real Google account
password in S-nail (for more on that see the section On URL syntax
and credential lookup).

But, how about XOAUTH2 / OAUTHBEARER?
Following up I cannot login to Google mail (via OAuth) one OAuth-based
authentication method is available: the OAuth 2.0 bearer token usage as
standardized in RFC 6750 (according SASL mechanism in RFC 7628), also
known as XOAUTH2 and OAUTHBEARER, allows fetching a temporary access
token via the web that can locally be used as a password. The protocol
is simple and extendable, token updates or even password changes via a
simple TLS secured server login would be possible in theory, but today
a web browser and an external support tool are prerequisites for using
this authentication method. The token times out and must be
periodically refreshed via the web.

Some hurdles must be taken before being able to use this method. Using
GMail as an example, an application (that is a name) must be
registered, for which credentials, a "client ID" and a "client secret",
need to be created and saved locally (in a secure way). These initial
configuration steps can be performed at
https://console.developers.google.com/apis/credentials. Thereafter a
refresh token can be requested; a python program to do this for GMail
accounts is https://github.com/google/gmail-oauth2-tools/raw/master/
python/oauth2.py:

$ python oauth2.py --user=EMAIL \
--client-id=THE-ID --client-secret=THE-SECRET \
--generate_oauth2_token
To authorize token, visit this url and follow the directions:
https://accounts.google.com/o/oauth2/auth?client_id=...
Enter verification code: ...
Refresh Token: ...
Access Token: ...
Access Token Expiration Seconds: 3600
$ # Of which the last three are actual token responses.
$ # Thereafter access tokens can regularly be refreshed
$ # via the created refresh token (read on)

The generated refresh token must also be saved locally (securely). The
procedure as a whole can be read at https://github.com/google/
gmail-oauth2-tools/wiki/OAuth2DotPyRunThrough. Since periodic timers
are not yet supported, keeping an access token up-to-date (from within
S-nail) can only be performed via the hook on-main-loop-tick, or (for
sending only) on-compose-enter (for more on authentication please see
the section On URL syntax and credential lookup):

set on-main-loop-tick=o-m-l-t on-compose-enter=o-c-e
define o-m-l-t {
xcall update_access_token
}
define o-c-e {
xcall update_access_token
}

set access_token_=0
define update_access_token {
local set i epoch_sec epoch_nsec
vput vexpr i epoch
eval set $i # set epoch_sec/_nsec of vexpr epoch
vput vexpr i + $access_token_ 2100
if $epoch_sec -ge $i
vput ! password python oauth2.py --user=EMAIL \
--client-id=THE-ID --client-secret=THE-SECRET \
--refresh-token=THE-REFRESH-TOKEN |\
sed '1b PASS;d; :PASS s/^.\{1,\}:\(.\{1,\}\)$/\1/'
vput csop password trim "$password"
if -n "$verbose"
echo password is <$password>
endif
set access_token_=$epoch_sec
endif
}

Not "defunctional", but the editor key does not work
Two thinkable situations: the first is a shadowed sequence; setting
debug, or the most possible verbose mode, causes a printout of the bind
tree after that is built; being a cache, this happens only upon startup
or after modifying bindings.

Or second, terminal libraries (see On terminal control and line editor,
bind, termcap) may report different codes than the terminal really
sends, rendering bindings dysfunctional because expected and received
data do not match; the verbose listing of bindings will show the byte
sequences that are expected. (One common source of problems is that
the -- possibly even non-existing -- keypad is not turned on, and the
resulting layout reports the keypad control codes for the normal
keyboard keys.)

To overcome the situation use for example the program cat(1) with its
option -v, if available, to see the byte sequences which are actually
produced by keypresses, and use the variable termcap to make S-nail
aware of them. The terminal this is typed on produces some unexpected
sequences, here for an example the shifted home key:

? set verbose
? bind*
# 1B 5B=[ 31=1 3B=; 32=2 48=H
bind base :kHOM z0
? x
$ cat -v
^[[H
$ s-nail -v -Stermcap='kHOM=\E[H'
? bind*
# 1B 5B=[ 48=H
bind base :kHOM z0

Can S-nail git-send-email?
Yes. Put (at least parts of) the following in your ~/.gitconfig:

[sendemail]
smtpserver = /usr/bin/s-nail
smtpserveroption = -t
#smtpserveroption = -Sexpandaddr
smtpserveroption = -Athe-account-you-need
##
suppresscc = all
suppressfrom = false
assume8bitEncoding = UTF-8
#to = /tmp/OUT
confirm = always
chainreplyto = true
multiedit = false
thread = true
quiet = true
annotate = true

Newer git(1) versions (v2.33.0) added the option sendmailCmd. Patches
can also be send directly, for example:

$ git format-patch -M --stdout HEAD^ |
s-nail -A the-account-you-need -t RECEIVER

Howto handle stale dotlock files

folder sometimes fails to open MBOX mail databases because creation of
dotlock files is impossible due to existing but unowned lock files. S-
nail does not offer an option to deal with those files, because it is
considered a site policy what counts as unowned, and what not. The
site policy is usually defined by administrator(s), and expressed in
the configuration of a locally installed MTA (for example Postfix
`stale_lock_time=500s'). Therefore the suggestion:

$ </dev/null s-nail -s 'MTA: be no frog, handle lock' $LOGNAME

By sending a mail to yourself the local MTA can use its normal queue
mechanism to try the delivery multiple times, finally decide a lock
file has become stale, and remove it.

IMAP CLIENT

[Option]ally there is IMAP client support available. This part of the
program is obsolete and will vanish in v15 with the large MIME and I/O
layer rewrite, because it uses old-style blocking I/O and makes
excessive use of signal based long code jumps. Support can hopefully
be readded later based on a new-style I/O, with SysV signal handling.
In fact the IMAP support had already been removed from the codebase,
but was reinstantiated on user demand: in effect the IMAP code is at
the level of S-nail v14.8.16 (with imapcodec being the sole exception),
and should be treated with some care.

IMAP uses the `imap://' and `imaps://' protocol prefixes, and an IMAP-
based folder may be used. IMAP URLs (paths) undergo inspections and
possible transformations before use (and the command imapcodec can be
used to manually apply them to any given argument). Hierarchy
delimiters are normalized, a step which is configurable via the
imap-delim variable chain, but defaults to the first seen delimiter
otherwise. S-nail supports internationalised IMAP names, and en- and
decodes the names from and to the ttycharset as necessary and possible.
If a mailbox name is expanded (see Filename transformations) to an IMAP
mailbox, all names that begin with `+' then refer to IMAP mailboxes
below the folder target box, while folder names prefixed by `@' refer
to folders below the hierarchy base, so the following will list all
folders below the current one when in an IMAP mailbox: `folders @'.

Note: some IMAP servers do not accept the creation of mailboxes in the
hierarchy base, but require that they are created as subfolders of
`INBOX' - with such servers a folder name of the form

imaps://mylogin@imap.myisp.example/INBOX.

should be used (the last character is the server's hierarchy
delimiter). The following IMAP-specific commands exist:

cache Only applicable to cached IMAP mailboxes; takes a message
list and reads the specified messages into the IMAP cache.

connect If operating in disconnected mode on an IMAP mailbox,
switch to online mode and connect to the mail server while
retaining the mailbox status. See the description of the
disconnected variable for more information.

disconnect If operating in online mode on an IMAP mailbox, switch to
disconnected mode while retaining the mailbox status. See
the description of the disconnected variable for more. A
list of messages may optionally be given as argument; the
respective messages are then read into the cache before
the connection is closed, thus `disco *' makes the entire
mailbox available for disconnected use.

imap Sends command strings directly to the current IMAP server.
S-nail operates always in IMAP `selected state' on the
current mailbox; commands that change this will produce
undesirable results and should be avoided. Useful IMAP
commands are:

create Takes the name of an IMAP mailbox
as an argument and creates it.

getquotaroot (RFC 2087) Takes the name of an
IMAP mailbox as an argument and
prints the quotas that apply to
the mailbox. Not all IMAP
servers support this command.

namespace (RFC 2342) Takes no arguments and
prints the Personal Namespaces,
the Other User's Namespaces and
the Shared Namespaces. Each
namespace type is printed in
parentheses; if there are
multiple namespaces of the same
type, inner parentheses separate
them. For each namespace a
prefix and a hierarchy separator
is listed. Not all IMAP servers
support this command.

imapcodec Perform IMAP path transformations. Supports vput (see
Command modifiers), and manages the error number !. The
first argument specifies the operation: e[ncode]
normalizes hierarchy delimiters (see imap-delim) and
converts the strings from the locale ttycharset to the
internationalized variant used by IMAP, d[ecode] performs
the reverse operation. Encoding will honour the (global)
value of imap-delim.

The following IMAP-specific internal variables exist:

disconnected
(Boolean) When an IMAP mailbox is selected and this
variable is set, no connection to the server is initiated.
Instead, data is obtained from the local cache (see
imap-cache). Mailboxes that are not present in the cache
and messages that have not yet entirely been fetched from
the server are not available; to fetch all messages in a
mailbox at once, the command `copy * /dev/null' can be
used while still in connected mode. Changes that are made
to IMAP mailboxes in disconnected mode are queued and
committed later when a connection to that server is made.
This procedure is not completely reliable since it cannot
be guaranteed that the IMAP unique identifiers (UIDs) on
the server still match the ones in the cache at that time.
Data is saved to DEAD when this problem occurs.

disconnected-USER@HOST
The specified account is handled as described for the
disconnected variable above, but other accounts are not
affected.

imap-auth-USER@HOST, imap-auth
Sets the IMAP authentication method. Supported are the
default `login' (called `plain' by some servers),
[v15-compat] `oauthbearer' (see FAQ entry But, how about
XOAUTH2 / OAUTHBEARER?), [v15-compat] `external' and
`externanon' (for TLS secured connections which pass a
client certificate via tls-config-pairs), as well as the
[Option]al `cram-md5' and `gssapi'. All methods need a
user and a password except `gssapi' and `external', which
only need the former. `externanon' solely builds upon the
credentials passed via a client certificate, and is
usually the way to go since tested servers do not actually
follow RFC 4422, and fail if additional credentials are
actually passed.

imap-cache Enables caching of IMAP mailboxes. The value of this
variable must point to a directory that is either existent
or can be created by S-nail. All contents of the cache
can be deleted by S-nail at any time; it is not safe to
make assumptions about them.

imap-delim-USER@HOST, imap-delim-HOST, imap-delim
The hierarchy separator used by the IMAP server. Whenever
an IMAP path is specified it will undergo normalization.
One of the normalization steps is the squeezing and
adjustment of hierarchy separators. If this variable is
set, any occurrence of any character of the given value
that exists in the path will be replaced by the first
member of the value; an empty value will cause the default
to be used, it is `/.'. If not set, we will reuse the
first hierarchy separator character that is discovered in
a user-given mailbox name.

imap-keepalive-USER@HOST, imap-keepalive-HOST, imap-keepalive
IMAP servers may close the connection after a period of
inactivity; the standard requires this to be at least 30
minutes, but practical experience may vary. Setting this
variable to a numeric `value' greater than 0 causes a
`NOOP' command to be sent each `value' seconds if no other
operation is performed.

imap-list-depth
When retrieving the list of folders on an IMAP server, the
folders command stops after it has reached a certain depth
to avoid possible infinite loops. The value of this
variable sets the maximum depth allowed. The default is
2. If the folder separator on the current IMAP server is
a slash `/', this variable has no effect and the folders
command does not descend to subfolders.

imap-use-starttls-USER@HOST, imap-use-starttls-HOST, imap-use-starttls
Causes S-nail to issue a `STARTTLS' command to make an
unencrypted IMAP session TLS encrypted. This
functionality is not supported by all servers, and is not
used if the session is already encrypted by the IMAPS
method.

SEE ALSO

bogofilter(1), gpg(1), more(1), newaliases(1), openssl(1), sendmail(1),
sh(1), spamassassin(1), iconv(3), setlocale(3), aliases(5), termcap(5),
terminfo(5), locale(7), mailaddr(7), re_format(7) (or regex(7)),
mailwrapper(8), sendmail(8)

HISTORY

M. Douglas McIlroy writes in his article "A Research UNIX Reader:
Annotated Excerpts from the Programmer's Manual, 1971-1986" that a
mail(1) command already appeared in First Edition UNIX in 1971:

Electronic mail was there from the start. Never satisfied with
its exact behavior, everybody touched it at one time or another:
to assure the safety of simultaneous access, to improve privacy,
to survive crashes, to exploit uucp, to screen out foreign
freeloaders, or whatever. Not until v7 did the interface change
(Thompson). Later, as mail became global in its reach, Dave
Presotto took charge and brought order to communications with a
grab-bag of external networks (v8).

BSD Mail, in large parts compatible with UNIX mail, was written in 1978
by Kurt Shoens and developed as part of the BSD UNIX distribution until
1995. This manual page is derived from "The Mail Reference Manual"
that Kurt Shoens wrote for Mail 1.3, included in 3BSD in 1980. The
common UNIX and BSD denominator became standardized as mailx(1) in the
X/Open Portability Guide Issue 2 (January 1987). After the rise of
Open Source BSD variants Mail saw continuous development in the
individual code forks, noticeably by Christos Zoulas in NetBSD. Based
upon this Nail, later Heirloom Mailx, was developed by Gunnar Ritter in
the years 2000 until 2008. Since 2012 S-nail is maintained by Steffen
Nurpmeso.

Electronic mail exchange in general is a concept even older. The
earliest well documented electronic mail system was part of the
Compatible Time Sharing System (CTSS) at MIT, its MAIL command had been
proposed in a staff planning memo at the end of 1964 and was
implemented in mid-1965 when Tom Van Vleck and Noel Morris wrote the
necessary code. Similar communication programs were built for other
timesharing systems. One of the most ambitious and influential was
Murray Turoff's EMISARI. Created in 1971 for the United States Office
of Emergency Preparedness, EMISARI combined private electronic messages
with a chat system, public postings, voting, and a user directory.

During the 1960s it was common to connect a large number of terminals
to a single, central computer. Connecting two computers together was
relatively unusual. This began to change with the development of the
ARPANET, the ancestor of today's Internet. In 1971 Ray Tomlinson
adapted the SNDMSG program, originally developed for the University of
California at Berkeley timesharing system, to give it the ability to
transmit a message across the network into the mailbox of a user on a
different computer. For the first time it was necessary to specify the
recipient's computer as well as an account name. Tomlinson decided
that the underused commercial at `@' would work to separate the two.

Sending a message across the network was originally treated as a
special instance of transmitting a file, and so a MAIL command was
included in RFC 385 on file transfer in 1972. Because it was not
always clear when or where a message had come from, RFC 561 in 1973
aimed to formalize electronic mail headers, including "from", "date",
and "subject". In 1975 RFC 680 described fields to help with the
transmission of messages to multiple users, including "to", "cc", and
"bcc". In 1977 these features and others went from best practices to a
binding standard in RFC 733. Queen Elizabeth II of England became the
first head of state to send electronic mail on March 26 1976 while
ceremonially opening a building in the British Royal Signals and Radar
Establishment (RSRE) in Malvern.

AUTHORS

Kurt Shoens, Edward Wang, Keith Bostic, Christos Zoulas, Gunnar Ritter.
S-nail is developed by Steffen Nurpmeso <s-mailx@lists.sdaoden.eu>.

CAVEATS

[v15 behaviour may differ] Interrupting an operation via SIGINT aka
`control-C' from anywhere else but a command prompt is very problematic
and likely to leave the program in an undefined state: many library
functions cannot deal with the siglongjmp(3) that this software (still)
performs; even though efforts have been taken to address this, no
sooner but in v15 it will have been worked out: interruptions have not
been disabled in order to allow forceful breakage of hanging network
connections, for example (all this is unrelated to ignore).

The SMTP and POP3 protocol support of S-nail is very basic. Also, if
it fails to contact its upstream SMTP server, it will not make further
attempts to transfer the message at a later time (setting save and
sendwait may be useful). If this is a concern, it might be better to
set up a local SMTP server that is capable of message queuing.

BUGS

When a network-based mailbox is open, directly changing to another
network-based mailbox of a different protocol (i.e., from POP3 to IMAP
or vice versa) will cause a "deadlock".

After deleting some message of a POP3 mailbox the header summary
falsely claims that there are no messages to display, one needs to
perform a scroll or dot movement to restore proper state.

In `thread'ed sort mode a power user may encounter crashes very
occasionally (this is may and very).

Please report bugs to the contact-mail address, for example from within
s-nail: `? eval mail $contact-mail'. Including the verbose output of
the command version may be helpful:

? wysh set escape=! verbose; vput version xy; unset verbose;\
eval mail $contact-mail
Bug subject
!I xy
!.

Information on the web at `$ s-nail -X 'echo $contact-web; x''.

illumos June 27, 2024 illumos