Say that someone knew a person of interest's full name and made a request to obtain certain information using someone's name who has permission/legal rights to view that material, and addressed that the info was sent to a specific address from which returned mail could be obtained by the poser. Given that this isn't identity theft and sending snail mail under another person's name to OR from 2 disclosed locations is legal, could the fact that the information is being read by someone unauthorized make it an illegal act itself? I ask because this is something hardly considered in law.
North American law in particular, specifically Anglophone laws for the most part.
I am certain that sending a request under someone else's name isn't illegal because millions of people do it all the time and it's the reason why people find unexpected bills and subscriptions from which they never recall signing up for. Also, if such a thing were illegal, it's unlikely anyone could prove it.
But this is besides the point.