Tribblix: manual page: aliases.5

ALIASES(5) File Formats and Configurations ALIASES(5)

NAME

aliases, addresses, forward - addresses and aliases for sendmail

SYNOPSIS

/etc/mail/aliases

/etc/mail/aliases.db

/etc/mail/aliases.dir

/etc/mail/aliases.pag

~/.forward

DESCRIPTION

These files contain mail addresses or aliases, recognized by
sendmail(8) for the local host:

/etc/passwd

Mail addresses (usernames) of local users.

/etc/mail/aliases

Aliases for the local host, in ASCII format. Root can edit this
file to add, update, or delete local mail aliases.

/etc/mail/aliases.{dir , pag}

The aliasing information from /etc/mail/aliases, in binary
ndbm(3C) format for use by sendmail(8). The program newaliases(8)
maintains these files.

/etc/mail/aliases.db

The aliasing information from /etc/mail/aliases, in binary,
Berkeley DataBase format for use by sendmail(8). The program
maintains these files.

Depending on the configuration of the AliasFile option in
/etc/mail/sendmail.cf, either the single file aliases.db or the
pair of files aliases.{dir, pag} is generated by newaliases(8).
As shipped with Solaris, sendmail(8) supports both formats. If
neither is specified, the Berkeley DataBase format which
generates the single .db file is used.

~/.forward

Addresses to which a user's mail is forwarded (see Automatic
Forwarding).

In addition, the NIS name services aliases map mail.aliases contains
addresses and aliases available for use across the network.

Addresses

As distributed, sendmail(8) supports the following types of
addresses:

Local Usernames

username

Each local username is listed in the local host's /etc/passwd file.

Local Filenames

pathname

Messages addressed to the absolute pathname of a file are appended to
that file.

Commands

|command

If the first character of the address is a vertical bar (|),
sendmail(8) pipes the message to the standard input of the command
the bar precedes.

Internet-standard Addresses
username@domain

If domain does not contain any `.' (dots), then it is interpreted as
the name of a host in the current domain. Otherwise, the message is
passed to a mailhost that determines how to get to the specified
domain. Domains are divided into subdomains separated by dots, with
the top-level domain on the right.

For example, the full address of John Smith could be:

js@jsmachine.Podunk-U.EDU

if he uses the machine named jsmachine at Podunk University.

uucp Addresses
... [host!] host!username

These are sometimes mistakenly referred to as ``Usenet'' addresses.
uucp(1C) provides links to numerous sites throughout the world for
the remote copying of files.

Other site-specific forms of addressing can be added by customizing
the sendmail.cf configuration file. See sendmail(8) for details.
Standard addresses are recommended.

Aliases

Local Aliases

/etc/mail/aliases is formatted as a series of lines of the form

aliasname:address[, address]

aliasname is the name of the alias or alias group, and address is the
address of a recipient in the group. Aliases can be nested. That is,
an address can be the name of another alias group. Because of the way
sendmail(8) performs mapping from upper-case to lower-case, an
address that is the name of another alias group must not contain any
upper-case letters.

Lines beginning with white space are treated as continuation lines
for the preceding alias. Lines beginning with # are comments.

Special Aliases

An alias of the form:

owner-aliasname : address

sendmail directs error-messages resulting from mail to aliasname to
address, instead of back to the person who sent the message.
sendmail rewrites the SMTP envelope sender to match this, so owner-
aliasname should always point to alias-request, and alias-request
should point to the owner's actual address:

owner-aliasname: aliasname-request
aliasname-request address

An alias of the form:

aliasname: :include:pathname

with colons as shown, adds the recipients listed in the file pathname
to the aliasname alias. This allows a private list to be maintained
separately from the aliases file.

NIS Domain Aliases

The aliases file on the master NIS server is used for the
mail.aliases NIS map, which can be made available to every NIS
client. Thus, the /etc/mail/aliases* files on the various hosts in a
network will one day be obsolete. Domain-wide aliases should
ultimately be resolved into usernames on specific hosts. For example,
if the following were in the domain-wide alias file:

jsmith:js@jsmachine

then any NIS client could just mail to jsmith and not have to
remember the machine and username for John Smith.

If a NIS alias does not resolve to an address with a specific host,
then the name of the NIS domain is used. There should be an alias of
the domain name for a host in this case.

For example, the alias:

jsmith:root

sends mail on a NIS client to root@podunk-u if the name of the NIS
domain is podunk-u.

Automatic Forwarding

When an alias (or address) is resolved to the name of a user on the
local host, sendmail(8) checks for a ~/.forward file, owned by the
intended recipient, in that user's home directory, and with universal
read access. This file can contain one or more addresses or aliases
as described above, each of which is sent a copy of the user's mail.

Care must be taken to avoid creating addressing loops in the
~/.forward file. When forwarding mail between machines, be sure that
the destination machine does not return the mail to the sender
through the operation of any NIS aliases. Otherwise, copies of the
message may "bounce." Usually, the solution is to change the NIS
alias to direct mail to the proper destination.

A backslash before a username inhibits further aliasing. For
instance, to invoke the vacation program, user js creates a
~/.forward file that contains the line:

\js, "|/usr/ucb/vacation js"

so that one copy of the message is sent to the user, and another is
piped into the vacation program.

The ~/.forward file can be used to specify special "per user"
extensions by creating a .forward+extension file in the home
directory. For example, with an address like jsmith+jerry@jsmachine,
the sendmail(8) utility recognizes everything before the "+" as the
actual username (jsmith) and everything after it, up to the "@"
symbol, as the extension (jerry) which is passed to the mail delivery
agent for local use.

The default value of the ForwardPath processing option in sendmail(8)
is:

O ForwardPath=$z/.forward.$w+$h:$z/.forward+$h:$z/.forward.$w:$z \
/.forward

where $z is the macro for the user's home directory, $w is the macro
for the local machine name and $h is the extension. For example, for
mail using the address, jsmith+jerry@jsmachine, the sendmail(8)
utility checks each of the four following file names, in the order
given, to see if it exists and if it has "safe" permissions, that is,
that neither the file nor any of its parent directories are group- or
world-writable:

~jsmith/.forward.jsmachine+jerry
~jsmith/.forward+jerry
~jsmith/.forward.jsmachine
~jsmith/.forward

The first file that meets the conditions is used to forward the mail,
that is, all the entries in that file receive a copy of the mail. The
search is then stopped.

FILES

/etc/passwd
Password file

/etc/nsswitch.conf
Name service switch configuration file

/etc/mail/aliases
Mail aliases file (ascii)

/etc/mail/aliases.db
Database of mail aliases (binary)

/etc/mail/aliases.dir
Database of mail aliases (binary)

/etc/mail/aliases.pag
Database of mail aliases (binary)

/etc/mail/sendmail.cf
sendmail configuration file

~/.forward
Forwarding information file

NOTES

Because of restrictions in ndbm(3C), a single alias cannot contain
more than about 1000 characters (if this format is used). The
Berkeley DataBase format does not have any such restriction. Nested
aliases can be used to circumvent this limit.

For aliases which result in piping to a program or concatenating a
file, the shell of the controlling user must be allowed. Which shells
are and are not allowed are determined by getusershell(3C).

February 25, 2017 ALIASES(5)