I need a good email spam filter

[ecchi]

Yes but this still relies on two untrue premises:

1. People who send spam do not spend time deconstruction the way the anti spam software works, in order to beat it.

2. All your friends are basically the same and all think alike, to a very small deviation from the group "norm". (a good example is that very few men are prepared to talk about erectile dysfunction, but a lot of spam does. So when a friend of yours gets depressed and writes to you for sympathy it will be tagged as spam. You won't see it, so won't reply, and your friend will go through life thinking that in his hour of need, you shunned him).

Also, I looked into a couple of spam filters using this method a while back (I get 1K+ spam a day). Maths was one of the few subjects I excelled at in school, and when you really studied the maths they quoted as "making them work" it was all gobbledygook hiding a basically flawed mathematical premise.