I think ejabberd or another other xmpp server would have been my first choice for a service like this by a long shot. If only we had some good iOS clients to go to. While I’m on android, most of the family and some of the friends use iOS, so it was kind of a non-starter from that alone.
Edit: log -> long
You use your email provider’s credentials to log into the app, which then creates an IMAP folder called delta-chat which houses all those conversations.
You’d verify it’s your mom by starting a chat with “[email protected]” she’d verify it’s you by making sure it’s coming from “[email protected]”