Over the years I've pretty much used every anti-spam measure in existence. The only
one I've found that actually works (and it is pretty much faultless, 100+ spams caught
daily, 0 false positives!) is SpamNet, this has recently become pay-ware ($3.99 a
month or $1.99 if you were a beat tester). I have recently bought two subscriptions
(work and home). It really is worth it...go on!
http://www.cloudmark.com.