So many interesting crypto ideas around mico-transactions and content curation. And somehow we haven't even solved simple things like email spam.

Require the sender to put up a mico-bond to have their message visible and if the receiver is annoyed by the mail they can slash the bond.

Done.

Pretty crazy that even the almighty Google‘s best answer is simply „filtering the good from the bad“ - sometimes with mixed results.

Building barriers before adoption is an uphill battle. For a large email provider, this could be a nice opt-in for users though.