An interesting product from a young company called Cloudmark addresses the spam explosion.

It works as an Outlook add-in that allows you to flag a message as spam and uploads a signature to the network, and thus helps other Cloudmark users to block the spam, in effect acting as a distributed peer-to-peer Brightmail.

It remains to be seen whether this system will be resistant to denial of service or poisoning attacks.

Update (2002-07-10): I’ve been trying it out for three weeks, and so far it looks pretty good. Out of 353 spam I’ve received, it successfully blocked 233. It also gave 3 false positives from permission marketing companies (Art.com and MyPoints), which is not absurd as they have very poor optout management. But it also flagged an IEEE newsletter as spam, which seems a little bit excessive. So, use with precaution.