Recently, several individuals (Bill Gates included) have been advocating buying “stamps” to send emails in an effort to stop spam. The two mechanisms for this would be an actual payment (a fraction of a penny), or giving up processor time (perhaps ten seconds) to solve puzzles. The cost would, they hope, put off potential spammers since sending out a million emails would either take too long or take thousands of pounds.
This idea is fundamentally flawed.
There are legitimate reasons for sending large volumes of emails: universities, organisations, corporations, mailing lists. They all utilise email to a great extend and would be hit in exactly the same place as the spammers. That would simply be unacceptable.
Additionally, processor time is cheap. The spammers buy a few more boxes and let them deal with the backlog of processor time. The cost of this is not prohibitively high.
Nice try though, but it just won’t work.