Sovereign domains aside, I'm betting on using nostr relays simply as an ephemeral storage that keeps nostr events persisted for free for 1-3 days tops. This happen to pair well with the fact that most...
You are under the impression that only Nostr relays do that. That is false, and they aren't even the best at it. But I am also not interested much to prove this so use whatever is working for you
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