@pfrazee threw together a demo app called PaulMail [1] that you can view in Beaker [0]. It's very simple and is just a proof-of-concept (messages are unencrypted, for example), but it does hint at possibilities there.
[1] hyper://1bc1faf01a22270fb5698a60e63ef7a596ad976457e6d9914a8fd56d87281917/