that's not the hard part. it's the out-of-band key exchange. (or key discovery/verification. so basically how to avoid the trust on first time use problem.)
The certificate contains email address as ID, and email is verified automatically or by an initial email verification (TOFU trust model).
If Google, Microsoft and Apple offer E2EE similar to Proton, the majority of email will be encrypted, as long as both sides use the same service, or globally if these companies share public keys for public key discovery.
Comments
that's not the hard part. it's the out-of-band key exchange. (or key discovery/verification. so basically how to avoid the trust on first time use problem.)
The certificate contains email address as ID, and email is verified automatically or by an initial email verification (TOFU trust model).
If Google, Microsoft and Apple offer E2EE similar to Proton, the majority of email will be encrypted, as long as both sides use the same service, or globally if these companies share public keys for public key discovery.