Info on what ProtonMail encrypts is here: https://protonmail.com/support/knowledge-base/what-is-encrypted/ https://protonmail.com/support/knowledge-base/what-is

Info on what ProtonMail encrypts is here: https://protonmail.com/support/knowledge-base/what-is-encrypted/ https://protonmail.com/support/knowledge-base/what-is-encryp... TL;DR: It encrypts just about everything in storage but "Subject lines and recipient/sender email addresses are encrypted, but not end-to-end encrypted.", which tells me they might have access to these things.