I must say that I’m very impressed with the automatic anti-spam filter that comes with WordPress – it is called Akismet. At this point in time, it has blocked 715 spam comments, and every one that I’ve checked it has been 100% correct on (and I’ve checked most of them)! I’m thinking of looking into how it works (if it is open source, which I imagine it is). I wonder if a similar system can be written for use on email spam and whether it would be as effective.