Comment by crawrey

You may want to consider German-based Tutanota (https://tutanota.com) who uses open-source cryptography, rather than some alternatives such as Swiss-based ProtonMail who use a combination of open-source and proprietary closed-source cryptography.

Failing that, head on over to https://privacytoolsio.github.io/privacytools.io/ and check out alternatives and other related information.