If starting over, proof-of-work might work. Nostr software has explored a number of spam prevention mechanisms. Some of them are quite good. But one that didn't gain widespread adoption was proof-of-work. I'm thinking of a PoW on public keys. If public keys must end in 28 zeroes or be rejected as invalid keys, this would require about 100 seconds of delay for someone to create a new identity. If handling a spam message takes only 10 seconds (probably less), then spammers would have to work 10x as hard as spam recipients to keep the spam flowing. That might not be enough to deter spammers entirely, but it would be an unavoidable cost in the equasion that could slow spam down. And of course other spam prevention techniques could also be in play, it doesn't interfere with any of them. What do you think? If this isn't useful, or makes something important too hard to do, let me know. This would be for mosaic, not nostr, since nobody uses mosaic it can get these kinds of changes.