Yesterday i tested “mailpile” on my Raspberry pi, easy installation, maby something to add to the packages.
Mailpile is an e-mail client!
Mailpile is a search engine and a personal webmail server.
Mailpile is an easy way to encrypt your e-mail.
Mailpile is software you run yourself, on your own computer.
https://www.mailpile.is/download/linux.html, easy to install on the pi with the debian linux instructions.