I was starting my research on creating a system using qmail and SpamAssassin to make an anti spam store and forward email server. I was on http://www.qmail.org checking out the latest info for qmail when I some how got to the page for the MailToaster
It has almost everything that I wanted straight out of the virtual box. It uses qmail has support for SpamAssassin and has some support for maintaining your users in MySql.
The system is based on a FreeBSD installation, but that means that you could write a MailToaster and create it into a full commercial product without too much effort. (Licensing issues are more relaxed on FreeBSD)
In any case, the docs and everything for the MailToaster look pretty good, so I’m going to see what it will take to set it up to do store and forward. If I can do that, then I have a new favorite toy 