Postfix resolves SMTP destinations via DNS, /etc/hosts, or it uses the transport map (which can be an SQL database or a local file).
If you cannot use DNS for multiple destinations, then you should
route ALL SMTP EMAIL through a smarthost. See:
http://www.postfix.org/BASIC_CONFIGURATION_README.html#relayhost
Oh, and please stop sending HTML-only mail to the mailing list.
That is utterly rude.
Wietse
