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."
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