The way I run it, email is private - but only when the other side has a similar setup, which is practically never :)

I like Protonmail too, it is a very good service.

Wish FreedomBox had an integrated mail server. 

 That's exactly the issue. The other side is (most likely) using gmail or similar and all email conversations get scanned. 

Practically nobody uses email e2ee. 

Just use signal/simplex for conversations.