I've used Y!Mail in the past, and been pleased overall. However, while their filters do catch about 95% of the Spam, I had problems with false positives. I, personally, would rather see a bit more pink meat in my mailbox and be assured that false positives would be very rare.

I've been pleased with GMail in this regard, but for real "industrial" use, I use Spam Assassin with a whitelist and a threshold score of 6.5. That seems to nab about 80-85% of the Spam, and I have had 0 false positives in about 6 months.

The only false positives I've experienced was when I accidentally marked one "mod_perl digest" as SPAM. It took about 5 trips to the SPAM folder to click "NOT SPAM" to start recieving the digest in my inbox again.

The onl things that slip past are

• bounce-backs, very annoying and the filter seems to filter them like other spam, instead of checking that the original sender is *.mail.yahoo.com, not some russian website.
• new nigerian 419 variations, but those are sooo easy to pick-off

MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"

I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).

** The third rule of perl club is a statement of fact: pod is sexy.