I installed Postgrey on our mail server yesterday and, to my surprise, cut our spam down to close to zero! I used to get hundreds of spams a day, but since yesterday, I’ve received two, both from the same sender. The (Bayesian) junk mail filter on my mail client did an admirable job, but I still had plenty of spam in my inbox to annoy me. I’m amazed that such a simple mechanism like greylisting actually works.