I don't think a centralized and by-default unencrypted XMPP server for all MPs would be a good solution. Signal isn't ideal either, as it requires sharing the

I don't think a centralized and by-default unencrypted XMPP server for all MPs would be a good solution. Signal isn't ideal either, as it requires sharing the phone number. I'm biased since I work for Threema, but any decentralized end-to-end encrypted messenger that does not require a phone number would be a good fit in my eyes. https://www.securemessagingapps.com/ https://www.securemessagingapps.com/ gives a good overview on the tradeoffs.