ORDB

From Wiki.openrbl.org

Open Relay Database

WARNING: Service Out Of Order
Article included for historical purposes only. [Template:Out_of_order]

http://it.slashdot.org/article.pl?no_d2=1&sid=08/03/25/2124224

Posted by kdawson on Tuesday March 25, @06:39PM

from the waking-the-dead dept. Chapter80 writes

"At noon today (Eastern Standard Time), the long dead ORDB spam identification system began returning false positives as a way to get sleeping users to remove the ORDB query from their spam filters. The net effect: all mail is blocked on servers still configured to use the ORDB service, which was taken out of commission in December of 2006. So if you're not getting any mail, check your spam filter configuration!"

Seriously managed since many years,
used by many commercial ISP.

Since ORDB only lists proven open relays there are nearly no false positives.