Zimbra is pretty much what you are after it sounds like. Just set it up once, and it just works. Just keep the OS updated and install any updates Zimbra releases. There is some manual work to get it going up front, but it's not hard.

The only way you can guarantee your email is kept private and not shared to any gov't agency or anything is to run it yourself. Then at least they have to serve you directly to get your emails ;P