Not sure I explained clear enough in the description above. My aim is not to spread SN contents, it's about find a way to notiy people that has already signup to invite them to come back.

The notifications aren't not about the contents. See it like a summary of all notifications delivered to your preferred login/signup medium

there's not 3rd one, it's a continuation, (skipping the first point about teh newsletter that has already been covered) fo example if you signup with X, and linked your nostr npub too, you could be able to select where to receive these DMs from the setting page