May be slightly off topic

For times when you can't do you own filtering/parsing (like hotmail) I have been using the free version of SpamCop with good results. Very good automatic header parsing, digging of URLs, talking to abuse.net to get abuse report address, automatic report generation etc. I almost feel like subscribing to their commercial service sometimes but I have managed to resist.

Disclaimer: I am not affiliated with spamcop.net in any way.

- Mushy (Just sharing info)