Postfix virtual ALIAS example: separate domains, UNIX system accounts

Postfix virtual ALIAS example: separate domains, UNIX system accounts

With the approach described in this section, every hosted domain can have its own info etc. email address. However, it still uses UNIX system accounts for local mailbox deliveries.

With virtual alias domains, each hosted address is aliased to a local UNIX system account or to a remote address. The example below shows how to use this mechanism for the example.com domain.

 1 /etc/postfix/main.cf:
 2     virtual_alias_domains = example.com ...other hosted domains...
 3     virtual_alias_maps = hash:/etc/postfix/virtual
 4 
 5 /etc/postfix/virtual:
 6     postmaster@example.com postmaster
 7     info@example.com       joe
 8     sales@example.com      jane
 9     # Uncomment entry below to implement a catch-all address
10     # @example.com         jim
11     ...virtual aliases for more domains...

Notes:

• Line 2: the virtual_alias_domains setting tells Postfix that example.com is a so-called virtual alias domain. If you omit this setting then Postfix will reject mail (relay access denied) or will not be able to deliver it (mail for example.com loops back to myself).

NEVER list a virtual alias domain name as a mydestination domain!

• Lines 3-8: the /etc/postfix/virtual file contains the virtual aliases. With the example above, mail for postmaster@example.com goes to the local postmaster, while mail for info@example.com goes to the UNIX account joe, and mail for sales@example.com goes to the UNIX account jane. Mail for all other addresses in example.com is rejected with the error message "User unknown".

• Line 10: the commented out entry (text after #) shows how one would implement a catch-all virtual alias that receives mail for every example.com address not listed in the virtual alias file. This is not without risk. Spammers nowadays try to send mail from (or mail to) every possible name that they can think of. A catch-all mailbox is likely to receive many spam messages, and many bounces for spam messages that were sent in the name of anything@example.com.

Execute the command "postmap /etc/postfix/virtual" after changing the virtual file, and execute the command "postfix reload" after changing the main.cf file.

Note: virtual aliases can resolve to a local address or to a remote address, or both. They don't have to resolve to UNIX system accounts on your machine.

More details about the virtual alias file are given in the virtual(5) manual page, including multiple addresses on the right-hand side.

Virtual aliasing solves one problem: it allows each domain to have its own info mail address. But there still is one drawback: each virtual address is aliased to a UNIX system account. As you add more virtual addresses you also add more UNIX system accounts. The next section eliminates this problem.