Hashcash is an interesting idea and very creative. But I do think you're right. It may impose reasonable limits on a single computer. But if an attacker has a b

Hashcash is an interesting idea and very creative. But I do think you're right. It may impose reasonable limits on a single computer. But if an attacker has a botnet they can still send out a crap load. Botnets and spam practically go hand-in-hand as-is, so I don't see how hashcash helps there. Still... it is a creative idea.