As far as I can remember, you don't even get IMAP access on the Proton free tier. For me, that's a non-starter. The privacy claims are also mostly marketing, as it is basically impossible to verify what Proton actually does when approached by a three-letter agency. I wouldn't use email anyway if I had something to hide, the email protocol wasn't designed with secrecy of communications in mind. For that, Signal seems far better, or perhaps a self-hosted, encrypted Matrix room.