If most recipients are remote. then use relay_domains and list the remote recipients in relay_recipient_maps.
virtual_alias_maps:
us...@example.com user1@localhost
relay_recipient_maps:
us...@example.com whatever
transport_maps:
example.com: [host.example.com]
and relay_domains=example.com
This is the http://www.postfix.org/STANDARD_CONFIGURATION_README.html
gateway example, plus cvirtual aliases for local recipients.
Wietse
