Greylisting

If you run a mailserver: If you're not greylisting yet, you should be. Man, what a difference in spam it makes! We implemented a greylisting addin for postfix, tumgreyspf (sorry, no link, you can Google it), and suddenly we have almost no spam. We were definitely getting more and more spam, I would get ~30 a day, and now I'm getting 1 or 2 a day. Eventually, the spam programs will start to mark domains that appear to be greylisting as doing so, and try again in 5 minutes, but it's an arms race, and for now this really helps.