> Charge $0.001 to deliver an email. Maybe in crypto or some kind of PoW. Legitimate senders won't care about $0.001.

So your solution to crypto people poisoning the well is something that will be incredibly inconvenient for everyone but crypto people?

Ah, I see it's time to deploy https://craphound.com/spamsolutions.txt again. I'm always sad that that document has aged so well.

Funny you'd say that, Bitcoin's PoW algorithm (hashcash) was originally precisely designed for that use case: https://en.wikipedia.org/wiki/Hashcash