for all intents and purposes email is not e2ee.
The intended payload can be in an header-less encrypted file on a throw-away SFTP server in the tmpfs ram disk.
I understand that metadata is valuable information for spies/governments and that encrypting or hiding it is valuable for privacy. But if you use that definition, there are almost no E2EE protocols on the planet in use.
First and foremost, any protocol that uses Apple or Google push notifications is giving metadata to those organizations. Even Whatsapp, iMessage, Signal, Telegram private messages, all of that leaks metadata but the contents of messages are hidden from the provider.
I know, right? I admit that is mostly for people on Linux desktops. People on smart phones are 100% monitored regardless of encryption or fake E2EE that platforms pinky promise is really E2EE like Signal. Shame on Moxie, he knows better.
Ovaltine has a crapload of sugar. Don't drink that horse piss.