If users are paying a relay or service for storing their events, they likely will want to re-publish their inbound DMs to that same service.

What’s interesting is that while the pubkey isn’t yours, technically it’s data you want to have access to and likely redundant or backed up.

How does this impact or influence relay data retention or usage quotas - not sure. A spammer could flood you with DMs and bloat your usage limit. Or your DM sender may now be using the same paid relay storage as you - or may stop paying one day and all DMs gone.

One approach could be if you AUTH to a relay, then it can persist that DM from another pubkey under your account or data usage limit (or just detect it is an inbound DM for you). You could then see events you re-published/broadcast/store from other pubkeys and manage that data. Great.

Next consideration is can the pubkey sender now delete your inbound DM on your paid relay with a kind 5?

Ha. Nostr is deceptively simple. The real world fights back.