Major ISPs Look To Sender Authentication To Block Spam

"Really, what this is about is taking the anonymity out of e-mail," said Ken Hickman, senior director for mail platforms at Yahoo.

The vendors in the Anti-Spam Technical Alliance said sender authentication can go a long way to help stop so-called "zombies," which are major sources of spam. "Zombies" are computers that have been taken over by hackers and used to send spam without the owners' knowledge. Frequently, the takeover happens when the computers are infected by viruses and worms.

AOL found in a recent study of its own mail traffic that zombies were responsible for 89 percent of spam it received, said Carl Hutzler, director of anti-spam operations for AOL. Likewise, Yahoo is finding that 40 percent of spam comes from zombie machines.

Spammers also have other means of taking over other people's computers, such as hijacking mis-configured web proxies and e-mail relay servers.

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These attacks succeed in part because e-mail recipients now have no reliable means of authenticating the sender of a message. In other words, the recipient can't verify that the sender of a message is who he claims to be.

As a means of solving that problem, the alliance endorsed two leading technologies for sender authentication: