I'm not familiar enough with the DM chat NIPs to answer this with any confidence. nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z and nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn and nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6 all know more than me about multi-party DM.
Discussion
I don't know if I follow? Can't you just send each as a separate event?
You could but if a big stack of DMs goes to a large relay they can rate limit or block, as it can look like spam.
cc: npub1ymt2j3n8tesrlr0yhaheem6yyqmmwrr7actslurw6annls6vnrcslapxnz
Just pick 2+ relays for your kind 10050 relay list and you should be good. Local backups are a good extra measure, either on a local relay or using a jsonl file.