ALIASES(5) File Formats Manual ALIASES(5)

aliases — aliases file for smtpd

This manual page describes the format of the aliases file, as used by smtpd(8). An alias, in its simplest form, is used to assign an arbitrary name to an email address or a group of email addresses. This provides a convenient way to send mail. For example an alias could refer to all users of a group: email to that alias would be sent to all members of the group. Much more complex aliases can be defined however: an alias can refer to other aliases, be used to send mail to a file instead of another person, or to execute various commands.

Within the file, ‘#’ is a comment delimiter; anything placed after it is discarded. The file consists of key/value mappings of the form:

key: value1, value2, value3, ...

key is always folded to lowercase before alias lookups to ensure that there can be no ambiguity. The key is expanded to the corresponding values, which consist of one or more of the following:

A user on the host machine. The user must have a valid entry in the passwd(5) database file.
/path/to/file
Append messages to file, specified by its absolute pathname.
|command
Pipe the message to command on its standard input. The command is run under the privileges of the daemon's unprivileged account.
:include:/path/to/file
Include any definitions in file as alias entries. The format of the file is identical to this one.
user-part@domain-part
An email address in RFC 5322 format. If an address extension is appended to the user-part, it is first compared for an exact match. It is then stripped so that an address such as user+ext@example.com will only use the part that precedes ‘+’ as a key.
error:code message
A status code and message to return. The code must be 3 digits, starting 4XX (TempFail) or 5XX (PermFail). The message must be present and can be freely chosen.

/etc/smtpd/aliases
Default aliases file.

smtpd.conf(5), makemap(8), newaliases(8), smtpd(8)

The aliases file format appeared in 4.0BSD.

February 13, 2021 Linux 6.10.10-arch1-1