Hmmmm. That got me thinking about spam, and I went off on a tangent. What if an email could be parsed in such a way as to generate seed data for an an NP probl

Hmmmm. That got me thinking about spam, and I went off on a tangent. What if an email could be parsed in such a way as to generate seed data for an an NP problem which the sender must solve and supply the answer in the in the email header... If the receiver can instantly dismiss any emails that provide an answer that can not be verified, then that could have a huge impact on the the spammers ability to send spam in the volumes they currently enjoy. A penalty of 5 seconds per email is unlikely to impact ordinary users, but would be a major pain for spammers. Also, could this be used to throttle user input to mitigate brute force attacks?