Daniel Lawson wrote:
It doesn't require a complete reimplementation at all - it is a plugin in your mail client and a plugin in the ISP's MTA.
If it is a plugin to your mail client then it is even less use. Until the scheme reaches sufficient penetration (estimate of 10 years according to one of the authors) that you can require mail senders to use it, spammers will simply use clients that don't implement it.
Spamassassin already uses hashcash for verifying email, so if you send mail with hashcash then it greatly reduces the chance that it's flagged as spam. As sammy was saying to me (in person), if you could get hotmail or gmail to adopt a scheme like this, then you suddenly have an assurance that thousands of people are not spammers, and spam suddenly becomes a lot more obvious. I personally think that something has to be done about the "spam problem" within the next 18 months or email is going to become useless to the average user. And while none of the solutions I've seen are anything like a "spam killer", I can see how many of them fit together to significantly reduce the level of spam that I receive on the Internet.