qpsmtpd - It could make for much nicer integration with spam filtering tools. I need to get cracking on my whole email infrastructure someday to get rid of spam. First task to see that whatever choice works with Cyrus and then start doing some research into server-side spam filtering. Client-side filtering mostly works, but even if it catches 90% a whole bunch still get through.
Note that there's also an SMTP server for POE