if you have lightning nodes attached to the relay that can receive keysend/AMP payments you can pay anonymously and load credit on a special pair of keys (you create and provide two secret keys to the sender that identify your messages as being associated with the account

then you construct 3 hop chains (or more) based on this and each goes to a different relay, the message is encrypted using the account key recognisable by its matching pubkey in the header and the relay then knows it can forward it as it's paid for, no spam problem

this is a perfect use case for it as a way to enable nostr relays to act as VPNs for paying users

anyway, just check out what i invented, of course i hope it gets used, i spent almost a whole year working on that, but didn't get to the actual testing phase, it's just a heap of unit tests with virtual relays and an encryption protocol and session payment protocol all written and tested