When I ran my own mail server, I enjoyed running Postfix. It is highly configurable and quite capable. I am not the biggest fan of RBLs, which this article mentions, among other techniques. I was please, though, to see the article really focuses much more on taking advantage of Postfix’s advanced configuration than relying on RBLs and the like. The initial point of the article is that really solely on filters, like SpamAssassin, can be a bit to CPU intensive for high volume servers. I think the techniques discussed are a great example of defense in depth, a technique of which I am particular fan.