After going through a fairly simple setup, SpamTitan just works. It does a great job of stopping most spam and has a small number of false positives. It is also pretty easy to set up notifications on any blocked emails to ensure that proper capture is occurring. One side feature that I really like is using the web interface to see what emails have been allowed through. Using that information, when a client calls and tells us they sent an email that we didn't get, I can immediately look on SpamTitan to see if the email reached our servers at all. This allows me to very quickly determine if an email that never reached us was blocked on by our servers or prior to reaching us at all.
