I'm not sure I understand all of the angles on this. I can see that online email services (like G-Mail, Yahoo Mail and Hotmail) are vulnerable to this, but I'm uncertain whether my own ISP, which holds emails until I download them to my computer, is also vulnerable. It would seem that since they electronically actually have those emails, they are just as vulnerable to the gaze of Inspector Morose as the online variety of email service.
Is there any sort of email setup that takes the third party out of the email equation completely?