It may interest you to know that not one piece of intercompany email at rsync.net has ever traversed any network. It's all just a local copy operation.[1] So, no encryption, but ... that's not relevant in this case.

The same could be true for your family, or small social circles that share an email server. If you use a secure mail client to connect to the server, and all mail on that domain doesn't traverse a network ... that's a win, even without "email encryption".