Check out GPGTools [0]... it integrates with macOS Mail.app to send encrypted and/or cryptographically signed emails.

They claim that it "integrates the power of GPG into almost any application via the macOS Services context menu. It allows you to encrypt/decrypt, sign/verify text selections, files, folders and much more."

[0]: https://gpgtools.org

e2e encryption takes google mostly out of the loop (except for the "meta" data)