Using Mail Aliases (Part 4):

The staff alias is a mailing list. A mailing list is simply an alias with multiple recipients. In the example, several people are responsible for maintaining this mail server. Messages addressed to root are delivered to all of these people through the staff mailing list.

Two special aliases are associated with the mailing list. The owner-staff alias is a special alias used by sendmail for error messages relating to the staff mailing list. The format that sendmail requires for this special alias is owner-list, where list is the name of the mailing list. The other special alias, staff-request, is not required by sendmail, but it is expected by remote users. By convention, manual mailing list maintenance requests, such as being added to or deleted from a list, are sent to the alias list-request, where list is the name of the mailing list.

The last eight lines are user aliases we added to the file. These lines direct mail received at the mail server to the computers where the users read their mail. These aliases can be in a variety of formats to handle the various ways that e-mail is addressed to a user. The first three lines that forward mail to norm@hawk.foobirds.org all illustrate this. Assume that this /etc/aliases file is on wren, and that the MX record in DNS says that wren is the mail exchanger for foobirds.org. Then, mail addressed to norman.edwards@foobirds.org would actually be delivered to norm@hawk.foobirds.org. It is the combination of mail aliases and MX records that make possible the simplified mail-addressing schemes used at so many organizations.