With email, you _can't_ encrypt the headers of message. Who the message is to, who it's from, when it was sent, what the subject line is... All those things nee

With email, you _can't_ encrypt the headers of message. Who the message is to, who it's from, when it was sent, what the subject line is... All those things need to be accessible to every server that touches the message from creation to delivery. Things get worse when you have to interoperate with mail clients that don't support encryption. Now the best you can do is encrypt the body of the message at rest, but you still have to be able to decrypt it to deliver it. You're absolutely right that _if_ both parties are using PGP in their clients, then the _body_ of the email will be secure, end to end (not the meta data mind you, just the body). However, that requires a lot of manual key management (assuming you use a client that supports it in the first place). That key management nightmare is why no one actually uses PGP...