The Subject is part of data; you can't say you want end-to-end encryption and agree that some parts of the content is in clear. I understand why you're saying

The Subject is part of data; you can't say you want end-to-end encryption and agree that some parts of the content is in clear. I understand why you're saying Signal is proprietary, but it's also the standard for encrypted messenger that scales. Any protocol (or group of protocol) aiming to provide encryption and claiming to protect privacy should be doing at least as much as Signal. That bar is impossible to reach with email, short of coming up with an incompatible protocol in which case we might as well do it proper... that's what XMPP is for ;)