[cpach]

I would love to see a sound implementation of secure e-mail, but I also believe that such a system should not be built on top of SMTP.

Signal’s cryptography seems stellar, but to me it feels a bit weird to use instant messaging as a full replacement for electronic letters. I’m guessing here, but it would probably not be impossible to build a more traditional e-mail client on top of the Signal Protocol.

[maxnoe]

I don't see why this should not be possible.

Isn't this mainly about adding a a subject metadata field an a client that just displays messages differently, enables sorting into directories and so on?

Is there a real technical difference between messaging and long form emails that I don't see?

[ForHackernews]

Email is based on open, federated protocols. Every successful instant messaging service (sorry XMPP) as been a single closed provider.