I don't think anyone should anyone else's letters or packages etc. Unless they expressly stated that it was okay to do so. Being a couple is no excuse to break this 'rule'.

Why would you avoid discussing it? He crossed a boundary, your boundary, and that is *not* okay. Again, being your husband is no excuse for him to 'disrespect' you or cross your boundary. Otherwise, he will keep doing it and you would end up building resentment and this could ultimately blow up. Address the issue now, as it arises. Don't let it fester.

I would tell him explicitly not to open packages etc. that aren't in HIS name. That is not okay.