sendmail, 4th Edition

Role in the aliases File

Aliasing is the process of converting one recipient name into another. One use is to convert a generic name (such as root) into a real username. Another is to convert one name into a list of many names (for mailing lists).

Take a few moments to examine your aliases file. Its location is determined by the AliasFile option in your sendmail.cf file. For example:

O AliasFile=/etc/mail/aliases

Compare what you find in your aliases file to the brief example of an aliases file listed here:

# Mandatory aliases.
postmaster:     bob
MAILER-DAEMON:  postmaster
abuse:          postmaster

# The five forms of aliases
John_Adams:     adamj
xpres:          ford,carter,reagan,clinton
oldlist:        :include:/usr/local/oldguys
nobody:         /dev/null
ftphelp:        |/usr/local/bin/sendhelp

Your aliases file is probably far more complex, but even so, note that the example shows all the possible forms of aliases.

Lines that begin with # are comments. Empty lines are ignored. As the first comment indicates, three aliases are mandatory in every aliases file. They are the simplest form of alias: a name and what to change that name into. The name on the left of the : is changed into the name on the right. Names are not case-sensitive. For example, POSTMASTER, Postmaster, and postmaster are all the same.^[11]

For every envelope that lists a local user as a recipient, sendmail looks up that recipient’s name in the aliases file. (A local user is any address that would normally be delivered on the local machine. That is, postmaster