In that case, the email provider that you use makes little difference at all. Because of the way that email works, it will always be visible in plain text (unless manually encrypted through PGP) by a third party other than the recipient at some point. There is of course the exception of, for example, direct communication happening between two Proton Mail accounts, but this is really hardly worth mentioning in any practical sense.
The long and short of it is that email should never be used for secure communications.
One can find interest in an objects technological design while still acknlowledging it's horror when put to practical use. They aren't mutually exclusive options.