I recently downloaded the newest version of Mozilla and noticed their new junk mail filters. Since I'm a nerd and I like to know how things work, I found the place on the mozilla website that referred to how their filters work. It's based on a algorithm found here:

http://www.paulgraham.com/spam.html

It actually makes a lof of sense even though I'm not a statistician. Maybe you could set up something like this on your mail box. You could always just use Mozilla, but what's tyhe fun in that? ;-)