PGP is great for privacy but rather hard to use for common users. I came up with a simple design that can be implement in main-string email system while preserving the usability.
Take Gmail for example.First Google should adopt zero-knowledge password proof for its account while asking users to choose recovery questions. To recover password, users will answer 3 secret questions and the password is encrypted with the answers. This ensures that users can recover password and get old emails back without letting Google know the password.