> Or you could become an American branch of any of the new ORBS', but I > think that would be something hogging bandwidth. Passive response detection. Have a deamon that watches your MTA's logfiles, and for every mailserver not already in the database as positive or negative, probe those mailservers for open relaying . Report back to a master server. Much less individual impact on the detection side than actively mass scanning the entire 'net. And detection is distributed. Hell, start up a sourceforge project and encourage everyone and their brother run the scanner, reporting back to the master server. (You'd of course want to have a username/password system to track whats coming from who, and keep track of troublemakers...) Now the downside of this is you won't find the open servers until they actually send a mail to one of the relay traps, but one mail is all it takes... Now you still need some bandwidth on the master server, but using DNS for querys was actually a pretty neat hack. Take advantage of a proven multilevel information caching tree system already in place...