free SPAM filters are not good enough (Score -1, Troll)

I've never found a free SPAM filtering system that even comes close to some of the commercial offerings. I mean these SPAM filters in the review can't even work right when the SMTP server is being used as a gateway server on a DMZ. They lack versitility. What I would like to know is how to make these freeby filters filter spam and then pass it on to an internal SMTP server for final delivery.