Mail is very often encrypted in transit. There is a lack of authentication, so a man-in-middle attack is often possible. But passively listening doesn't work.

Mail is very often encrypted in transit. There is a lack of authentication, so a man-in-middle attack is often possible. But passively listening doesn't work. It is not clear how mail should be stored at rest. A mail server at your own home is one solution. Encrypting all mail with pgp another. Neither solution is likely to scale in the coming years. Maybe it is better to say truely private things only over encrypted chat at the moment.