I thought I would post and see what people's experience has been with various spam filtering tools. A few comments:

1. I see spam as a law enforcement problem. The VAST majority of the spam I receive contains forged headers and is being relayed through systems without permission. If the government simply enforced the laws it already has, it could prosecute these people for computer fraud. This would eliminate most of the problem that I see. The reason that I get all this spam is because the government won't enforce their laws. (Although they are happy enough to raid internet "bong" dealers. Gosh I'm glad to be safe from them.)

2. I have one email address that is basically useless because of spam. For every legitimate email I receive there, I get 30 or more spams. My other email address is rapidly approaching this state.

3. The basic requirement for a spam filtering solution that I have is no false positives. I can deal with deleting some spam. Its not THAT big of a deal. If I could delete LESS spam, and still get all of my legitimate email, I think I'd be alright.

4. I don't trust RBL based solutions. RBLs block legitimate mail. Lots of it. I'm interested in blocking SPAM, not people who are using SMTP relay. This effort to lock down SMTP has been going on for years, and the amount of spam has not been reduced.

5. My only experience with "AI" like filters has been the spam filter in MacOSX. It doesn't work. It ids spam as legit. More importantly, it regularily IDs legit email as spam. I'm not sure how it measures up with other filters. If I put more effort into training it, it might get better, but I could never TRUST that if I turned it on it would never block legitimate email.

6. This morning I was considering implementing Challenge Response for all of my email. This sounds like an effective solution. Unfortunately, its not. The problem is that there are a number of bots out there, mostly related to ecommerce sites, that I probably do need to see email from. I can try to list them in my whitelist, but I risk missing something.

7. It occurs to me that what might work better then these solutions is something that relies on a network. If 100 people get the same email, its probably spam. This, I imagine, is what yahoo is doing. I think I've heard of systems that allow large numbers of people to coordinate to filter spam, but I don't recall what it is.

What systems are you using? How effective are they?