Add new virtual domain and alias

[admin]

suppose to register domain foo.com:

edit main.cf:
mydestination = $myhostname, localhost.$mydomain, localhost, foo.com
virtual_maps= hash:/etc/postfix/virtual_maps


add an alias pippo@foo.com and redirect all the mail to existent Unix user gianni:
edit /etc/postfix/virtual_maps
foo.com DOMAIN
fisrt@foo.com realuser@loaclhost
second@foo.com realuser@localhost
pippo@foo.com gianni@localhost

launch...
/usr/sbin/postmap /etc/postfix/virtual_maps
/etc/rc.d/init.d/postfix restart

..enjoy