[camiller]

Well, you should be able to encrypt the subject/body of the email without encrypting the headers, so the mail vendor never sees the content of the email, only the to/from addresses and such. But that encryption has to happen in the browser/application. ie Mailvelope plugin for Chrome and others like it. and I think there is an android mail client that will also do pgp/gpg encryption/decryption.

[dpark]

Sure. You could absolutely have an entirely different protocol that doesn't work with all the existing email clients/services out there. It's certainly been done multiple times. Obviously it's not caught on, though, because compatibility is sort of a big deal.