Delivering some but not all accounts locally

A drawback of sending mail as "user@example.com" (instead of "user@hostname.example.com") is that mail for "root" and other system accounts is also sent to the central mailhost. In order to deliver such accounts locally, you can set up virtual aliases as follows:

1 /etc/postfix/
main.cf:
2     
virtual_alias_maps = hash:/etc/postfix/virtual
3 
4 /etc/postfix/
virtual:
5     root     root@localhost
6     . . .

Translation:

• Line 5: As described in the virtual(5) manual page, the bare name "root" matches "root@site" when "site" is equal to $ myorigin, when "site" is listed in $ mydestination, or when it matches $ inet_interfaces or $ proxy_interfaces.