MacMinute just posted about a new spam-fighting tool called GoodbyeSpam.
According to their FAQ, here’s how it works:

GoodbyeSpam’s approach is simple, yet ingenious: Upon receiving a message from a Sender or Domain not previously Approved or Blocked by you, it quarantines the message and sends an email to the Sender. If you subscribe to GoodbyeSpam’s Home version (or Professional version with the Security Level set to Normal) the email simply asks them to click on a link. When they do, their message is released from quarantine and they are added to your Approved list so that future messages go right through.
While simply clicking on a link is easy for a real person, it’s not for a spammer. Since spammers frequently use invalid return addresses, they never receive GoodbyeSpam’s email. And, the spammers who do receive them have no automated way to respond. They must open and deal with each individual verification requests, which defeats their purpose for spamming in the first place!

Sounds like a pretty good idea — it’s like a “safe-list” (a la Hotmail), except the management is automated. Cool! Don’t think I’ll sign up just yet, though — .Mac‘s built-in junk-filtering, combined with the Jaguar version of Mail has been a killer anti-spam combo so far.