> In a nutshell, both Brian and I think that the choice is between
> Qmail and Postfix and that Qmail is probably better but it has a
> bizarre license and can be a pain to upgrade. I recommend that
> you read Brian's comment!

 We just had a discussion on spam-l (you need to be subscribed to access
 the list archive) about qmail. One particular problem appears to be
 that qmail (without patches) can only bounce messages to non-existent
 addresses, not reject them at smtp level. Considering that of all the
 spam we reject, between 75% and 90% is targeted at non-existent addresses,
 such behaviour causes a massive amount of additional, unnecessary traffic.

 YMMV.