In my quest to run my own mailserver on OS X, I looked at qmail (very complex), postfix (medium complex), and then finally found james. James is an Apache SMTP/POP server that is fully programmable in Java. It setup in about 30 seconds on OS X just by following the instructions on the website.
I set it up to use SMTP authorization and even tested it on ordb.org (to make sure it wasn't an open relay) with positive results.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031102025347362