As I'm collecting a bit of info in an effort to reduce spam etc on our servers, I thought I'd post a couple of them as there's some good articles out there that I hadn't read before.
First off, aAn interesting article on Dominopower called Hacking Domino mail rules to fight spam. It gives a good look into the inner workings of the Domino mail rules, and shows you how to make a few customisations.
Some pre-requisite reading for anyone who hasn't used the server side rules much: Using Domino 6 messaging settings to block spam and Using server mail rules to secure your mail system.
Even though the content of the above 2 articles is somewhat basic, there's still some good stuff in there. The little gem I found was the notes.ini variable SMTPExpandDNSBLStats=1 which I'd never heard of previously.
Another great resource is Chris Linfoots Domino Anti-Spam Architecture article, as well as pretty much everything on his site.
Finally, a few of you might have tried kSpam - previously I havent played with it, as our production box here runs on a Linux server (stop laughing - now you know why I hate Linux so much), however now there is a beta of kSpam for Linux up on OpenNTF. As usual, you need to be registered to download.