I ordered an old cookbook on Ebay and when it arrived an ink stamp on the package raised my eye brows. "media mail subject to inspection" in red letters right across the front. Now why does the post office have issues with a 100 page booklet titled "War-time baking" from the WWII era?
So with a little Googling(is that a word?) I found what the stamp meant. Seems they are pushing a new cheaper way to mail media, but there is just one small issue. You must let them inspect it.
2.3 Postal InspectionCheaper, but at what cost. I would rather have spent a few dollars more for privacy. But what a shame when we have to pay for privacy in this country.
Media Mail is not sealed against postal inspection. Regardless of physical closure, the mailing of articles at Media Mail rates constitutes consent by the mailer to postal inspection of the contents. [E710.1.3]