Notary plugin for Electrum Nostr is the first decentralized social messaging protocol to be successful, thanks to its seamless architecture. However, one remaining issue is spam: How can relays prevent malicious actors from uploading petabytes of undersired generated content? Here we propose a spam filter based on proofs of monetary sacrifice, that can be redeemed by the Bitcoin miners. Users decide how much fee they attach to Nostr events. Relays filter out events that have not received enough fees. Users set a fee threshold under which they do not wish to see content posted by others. This sets a price for spam, and creates a market for attention. #bitcoin #nostrevent #notary #withepaper https://github.com/spesmilo/notary