HashCash, one of the moving parts of Bitcoin, was itself invented by Adam Back as a way to fight spam. In essence, it’s a proof of work. So an email would requ

HashCash, one of the moving parts of Bitcoin, was itself invented by Adam Back as a way to fight spam. In essence, it’s a proof of work. So an email would require a tiny amount of “work” to be received. For one email this is no hindrance at all. But at spam scale it becomes a true hindrance.