This is Not a Brain Surgery

11:43 am - hashcash, Outlook Postmark

Without much fanfare Microsoft have included in OutLook 2007 a Postmark feature which is using "Math Puzzle" for SPAM control:

"A new Outlook E-mail Postmark feature aims to make it easier for other Outlook 2007 users to receive legitimate messages that might otherwise be classified as spam. When a user sends a “spammy” message, Outlook performs the calculations necessary to solve a simple computational puzzle and adds information about the puzzle and the solution to the SMTP message header. Because that computation takes only a little time for one message or a few messages but would take a very long time for a spammer sending millions of messages, the presence of an Outlook E-mail Postmark in the message header is a strong indication that the message isn’t spam."

[1]

This is basically an implementation of old good HashCash idea. I think this is great that they are doing this. This is one of few ways which allows to combat zombie computers sending spam email. I wish this implementation become more mainstream in other mail clients.

However, there are several problems with Microsoft approach. The first is that a Postmark feature is switched off my default [2]. The second is that according to some reports[3], Microsoft owns a patent on this technology, which could stop its adoption by other email software vendors. I also have not found a clear technical specficaiton of Postmark implementation, which could be used, for example, to add postmark checking to SpamAssassin.