I have been using this package for about a month and I works great. The best part is that is learns (looks for patterns).
and all the message that it considers as SPAM are placed in a folder, upon inspection, you can drag a file from the SPAM folder back into the inbox and the software remembers that action and re-trains itself.  So far it has been perfect all message that were sent to the SPAM folder were in fact SPAM.  It only took me about 10min to set it up and train it.

http://www.computerworld.com/securitytopics/security/story/0,10801,83689,00.html

Take Care

I hopes this is a help.