The thing with email is it's only encrypted (even in transit) sometimes. So it kinda has the same issue as iMessage. If you're a Gmail user using Gmail's web ap

The thing with email is it's only encrypted (even in transit) sometimes. So it kinda has the same issue as iMessage. If you're a Gmail user using Gmail's web app to email another Gmail user, you get encryption in transit (and it sounds like you might be able to implement E2EE as well). But if you email dave@somerandomemailserver.com, you won't know until you send the message whether it's encrypted. As for envelopes and wax seals--it's an interesting question. It requires a lot less technical knowledge for someone to open that envelope than to spy on messaging traffic. On the other hand, a lot more people have access to the messaging traffic and can bring scripts to bear on it at scale.