Open Relay Black List ORBL is an auto adjusting spam filter. ORBL watches current incoming Internet email traffic for spam signatures and adapts to block spam coming from open mail relays. http://www.orbl.org/
Open Relay Blackhole Zones ORBZ publishes , via DNS, a list of IP addresses of machines that they know to be open relays, even if they haven't yet been used to relay spam. http://www.orbz.org/