This makes me think that all client developers making use of DMs need to understand what an inbox relay is, and how to find out what it is for a user, and hope that they can send to it?
Discussion
I suspect so.
It's not a bad idea to do this to help increase likelihood of message being read. Certainly better then spamming/blasting to all relays, even if it does create more short lived network connections
Good news is I can find your relays from querying relay.damus.io
wss://chorus.mikedilger.com:444 (read, write)
wss://nos.lol (write only)
wss://nostr.einundzwanzig.space (read, write)
wss://nostrue.com (write only)
wss://offchain.pub (read, write)
Posting what I've found on this so that others who are curious may have something to go on...
The closest I've found on this "inbox relay" is an inference based on NIP 65 suggestions `DMs SHOULD only be broadcasted to the author's WRITE relays and to the receiver's READ relays to keep maximum privacy.`
https://github.com/nostr-protocol/nips/blob/master/65.md#final-considerations
So for each user you want to send a message to, before doing so, may need to first request all 10002 for that target pubkey from whatever relays you normally read from, and then parse for those that are not marked strictly for "read" purposes? Or maybe the suggestion is written backwards since they will be reading from that relay. Probably best to just try to push the DM to all the relays the user has announced in their 10002 event, and ignore any relay error messages as temporal.