Earlier quoted context omitted.
Use GPG. Don't use smartphones, don't use any closed software (especially non-free OSes.) Vote.
GPG doesn’t solve the problem of metadata surveillance. One of the major problems with technological solutions to privacy problems is that metadata surveillance is extremely useful to begin with, and it’s hard to make communication anonymous.
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-me...
[1] https://en.wikipedia.org/wiki/Cypherpunk_anonymous_remailer