thanks for your answer. You are right, this it a feature request, sorry.
I also use another backup product that works in the way I descibed before: the operator has full access to the data but he only can restore the item (no double click is possible on it) to the user mailbox or to a PST file.
Obviously he can restore the message to a pst and open it using outlook but the procedure is more hardworking and if performed voluntarily, it may be considered a violation of the privacy with intention, not a simply inadvertence.
I think that this feature could be interesting.