Or use Hashcash, which is a proof-of-work algorithm created for anti-DoS and anti-spam, and the inspiration of Bitcoin's mining algorithm. It's possible the bo

Or use Hashcash, which is a proof-of-work algorithm created for anti-DoS and anti-spam, and the inspiration of Bitcoin's mining algorithm. It's possible the botnets are strong enough to create Hashcash or mine Bitcoin and still spam enough to annoy us... and it would probably take either Google, Yahoo, or Microsoft announcing they would stop accepting legacy emails (where "legacy" could just be ones without Hashcash or BTC), for anyone to make a change.