For what it's worth, implementations like Delta Chat support encrypted subject lines[0]. Also, it would be relatively simple for mail providers to act as two h

For what it's worth, implementations like Delta Chat support encrypted subject lines[0]. Also, it would be relatively simple for mail providers to act as two halves of a Cypherpunk remailer[1]. By that I mean that when alice@sender writes an email to bob@recipient, the sender server only sees "remailer@recipient" as the recipient and the recipient server only sees "remailer@sender" as the sender. That approach just requires some onion-layering of the emails with encryption, and a reserved key-pair advertised per mail server. [0] https://delta.chat/en/help#how-does-delta-chat-protect-my-metadata https://delta.chat/en/help#how-does-delta-chat-protect-my-me... [1] https://en.wikipedia.org/wiki/Cypherpunk_anonymous_remailer https://en.wikipedia.org/wiki/Cypherpunk_anonymous_remailer