sendmail's alias database is usually kept in flat-text format in the file /etc/aliases. The file consists of commented lines (starting with #) and any number of key and value pairs, one per line, delimited by a :. So, for example:
# RFC 822 requires that every host have a mail address "postmaster" postmaster : rootThis aliases postmaster to root, so that any mail sent to postmaster will instead be delivered to root.
Aliases can also be redirected to a file, like this:
# Aliases to handle mail to msgs and news nobody : /dev/nullOr piped to a program, like this:
# an automatic bug-registering database program-bugs: |/usr/local/bin/program-bug-trackerYou can also specify multiple places to redirect mail by seperating them with commas:
# a makeshift mailing list project-list: email@example.com,firstname.lastname@example.org,email@example.comThus, a mail to project-list will be forwarded to all of the addresses listed.
sendmail cannot directly read this flat-text version of the aliases file. Instead, it converts this to a binary database (either DB or DBM, depending on which you compiled it with) when you use the newaliases command. Every time you make changes to /etc/aliases, you must run newaliases to update the database.