ALIASES(5)

NAME
aliases, addresses, forward - addresses and aliases for sendmail(8)

SYNOPSIS
/etc/passwd
/etc/aliases
/etc/aliases.dir
/etc/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/aliases
    Aliases for the local host, in ASCII format. This file can be edited to add, update, or delete local mail aliases.
/etc/aliases.{dir,pag}
    The aliasing information from /etc/aliases, in binary, dbm(3X) format for use by sendmail(8). The program newaliases(8), which is invoked automatically by sendmail(8), maintains these files.
~/.forward
    Addresses to which a user's mail is forwarded (see Automatic Forwarding, below).

In addition, the Network Information Service 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. These are listed in the local host's /etc/passwd file.

•   Local filenames. When mailed to an absolute pathname, a message can be appended to a file.

•   Commands. 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.

•   DARPA-standard mail addresses of the form:

        name@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. Top-level domains include:

        .COM
            Commerical organizations.
        .EDU
            Educational organizations.
        .GOV
            Government organizations.
        .MIL
            Military organizations.

    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(1C) addresses of the form:

        ... [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 configuration file. See the sendmail(8), and for details. Standard addresses are recommended.

ALIASES

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

    name: address [, address]

name 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 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

directs error-messages resulting from mail to alias-name to address, instead of back to the person who sent the message.

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
Normally, 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/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 user name for John Smith. If a .SM 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 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(1) 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(1) program.

FILES
/etc/passwd
/etc/aliases
~/.forward

SEE ALSO
uucp(1C), vacation(1), dbm(3X), newaliases(8), sendmail(8),

BUGS
Because of restrictions in dbm(3X) a single alias cannot contain more than about 1000 characters. Nested aliases can be used to circumvent this limit.