Think of the Czech Republic and depending on your frame of mind, images of fantastic architecture, beautiful women, or a long and rich cultural heritage might flicker through your thoughts. For me, though, when I think of the Czech Republic, I think of Lukas Gebauer (and I apologize now for not getting the accents in his name right).
Lukas is a software developer, and a very clever one indeed. He wrote the SpamHalter Bayesian spam filter for Pegasus Mail, and has written numerous plugins for Mercury, three of which (SpamHalter, ClamWall and GreyWall) are now standard components in the Mercury distribution. What probably amazes me more than anything else about Lukas is that he has written these very high-quality programs with almost no assistance from me - not that I wouldn't have been glad to provide it, but he seemingly hasn't needed it! I doubt I could have written code to use my own interfaces with so little assistance, so his work is all the more special because of that.
His latest plugin, GreyWall, is possibly the most startling plugin you'll ever encounter for Mercury. It uses a new event interface I developed for Mercury/32 v4.5, and simply turns away any connections from unknown server/sender combinations with a temporary (400-series) error. For real mail, all this means is that the first message from a particular server may take a few extra minutes to be delivered (all subsequent mail goes through with no delays). For spam zombies, however, the effect is quite dramatic. Current generation spam zombies are not set up to handle retry conditions - if they get one, they typically just skip the address and move on: this means that enabling GreyWall will result in a huge amount of your incoming spam being "turned away at the door", costing you no bandwidth, time or processing power. Experience in the test team has shown that enabling GreyWall can reduce spam levels by up to 90% even with no other filtering in place, and with a near-zero false positive rate!
As I noted above, GreyWall is now a standard part of Mercury, installable directly from the Mercury installer. When you decide to install GreyWall, or SpamHalter, or ClamWall, think of the Czech Republic and of Lukas, and consider going to his site to offer a little financial support to him: he's a very rare breed, and we all benefit from his work.
-- David --
May 6 2007