spam can be handle it with some new NIP that will force to pay to the destination a x amount in order to receive the "email like" message.
Call it here nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6
Discussion
I think that's undue friction and overhead at a per message level, whereas economically sound relays would be part of the social graph and whitelisted for forwarding messages.
Paid relays > paid messages
Same principle though, free doesn't work
I could receive free messages over public free relays.
But important ones could be over private nostr relays, maintained by myself or my trusted peers with which I maintain a certain volume of private messages.
Private relays could be configured also to be free for trusted peers. For others could be configured to be pay-to-send-msg.
Paying to send a message could be a subset of relay whitelisting into a social graph in that context... tiering like this would actually be consistent with QoS principles already used on the internet
my relay already by default (actually, i don't plan on changing this) doesn't allow reading of messages of a sensitive nature without being party to the conversation
yes, such a protocol could exist, i'm not 100% sure yet but i am pretty sure that you can, in principle, make a relay require an immediate zap in order to release an authentication lock