Interesting reference. See who is sending spam on your, or any other, domain.

A new Web site aims to help determine whether a specific computer has been sending legitimate e-mail or spam.

The TrustedSource Web site uses data from reputation filters, which are billed as the next big thing in e-mail security. Makers of spam-fighting tools collect data on e-mail senders and use that to assign "reputations" to e-mail sending computers and Internet domains. Those who send a lot of spam get a negative rating and their messages are more likely to be filtered out.
The Web site is designed to be a reference tool. Entering a domain, for example--generates a list of the Internet Protocol addresses of machines that send e-mail for that domain. Users can then drill down and click on each sending address to see if the specific machine has been sending junk mail or legitimate messages.
Through data received from the Companys global network of IronMailŽ appliances, which protect more than 10 million enterprise e-mail inboxes, the ZombieMeterSM tracks the number of new, completely unique zombies per hour, every hour. Visitors can view real-time updates regarding new zombie activity across the world, including the origination of messages and the number of machines affected by zombie activity.
cnet news :: Joris Evers :: August 29, 2005