...blacklist entire Gmail servers due to their inability to obtain the real sender’s IP. It’s a signal from the anti spamcommunity, and since Gmail will continue not revealing the real sender’s IP, something they’ve received a lot of criticism...
http://blogs.zdnet.com/security/?p=1514
...email addresses besides their probes? If the service is leveraged, then LashBack will contact members of the anti-spamcommunity to add other types of honey pot and other seed email addresses into the system. This is done to protect consumers...
http://www.lashback.com/LashBack%20Lead%20Source%20Validator.pdf