Well... Hard to strike the balance between paranoia and a wise degree of caution...

Yeah, I wouldn't send him anything personal to an address where other members of his family had access to the account.

I wouldn't send him anything personal from an address where my employers etc have access to the account either. I know that people have lost their jobs because of their employers reading their outgoing / incoming mail (therapy sessions).

I'm not sure about encryption and the like... I don't really understand what all that is about.

I think it is about how easy / hard it is to intercept someones mail.

I'd also want to know what t is planning on doing with the conversations. Merge them together to make a book? Print them out on paper and put them in his filing cabnet? Agree never to show anybody else without my permission (and accept that they would have to do so if ordered by a judge or whatever too)