From the DMM section 173 .4 The sections about commercial mail are identical, but under different sections. (373 and 473)
http://pe.usps.com/text/dmm300/173.htm#1113611
4.0 Content Standards for Media Mail
4.1 Qualified Items
Only these items may be mailed at the Media Mail prices:
a. Books, including books issued to supplement other books, of at least eight printed pages, consisting wholly of reading matter or scholarly bibliography, or reading matter with incidental blank spaces for notations and
containing no advertising matter other than incidental announcements of books. Advertising includes paid advertising and the publishers' own advertising in display, classified, or editorial style.
My friends magazine was inspected in transit, not at his post office. They may have backed off inspections, but all media mail is considered "open" and subject to inspection. (173.2.2)
2.2 Postal Inspection
Media Mail and Library Mail are not sealed against postal inspection. Regardless of physical closure, the mailing of articles at Media Mail or Library Mail prices constitutes consent by the mailer to postal inspection of the contents.
I tried to claim the baseball cards under 173 .4.g But they weren't going for it. A different post office might. But then, if it get inspected along the way it could still be returned.
g. Printed educational reference charts designed to instruct or train individuals for improving or developing their capabilities. Each chart must be a single printed sheet of information designed for educational reference. The information on the chart, which may be printed on one or both sides of the sheet, must be conveyed primarily by graphs, diagrams, tables, or other nonnarrative matter. An educational reference chart is normally but not necessarily devoted to one subject. A chart on which the information is conveyed primarily by textual matter in a narrative form does not qualify as a printed educational reference chart for mailing at the Media Mail prices even if it includes graphs, diagrams, or tables. Examples of qualifying charts include maps produced primarily for educational reference, tables of mathematical or scientific equations, noun declensions or verb conjugations used in the study of languages, periodic table of elements, botanical or zoological tables, and other tables used in the study of science.
I've also mailed stuff media mail that sort of qualified. But I stopped using it for ebay stuff unless it qualified. Just too much risk of an added expense and a delay that a buyer would likely blame me for.
I've also had a first class parcel returned because it fell into an odd classification limbo. It was too ridgid to count as a letter or flat, so it had to be a package. So it got delivery confirmation through click and ship. But they rejected it because it wasn't 3/4 of an inch thick, which is the minimum for delivery confirmation. In the end I repacked it with a packing peanut making it thick enough and reused the label. (Technically not allowed, but approved because of the loophole - They wanted postage to make it priority, I wanted a refund since they were saying it wasn't a package - Adding thickness and reusing the label was a compromise that made the problem go away) The buyer was a government official, and was very understanding.
After them looking up 16mm film in the DMM for media mail a couple times the clerks at my local branch don't question me much anymore about what class I'm using or wether the contents qualify. They even had me advise another customer on how to pack a pennant.
Steve B
PS: Since I collect stamps and odd usages, if anyone works for an antivenin lab that recieves live scorpions........I'd really like one of the empty boxes for my collection. Yes, you can mail scorpions under the right conditions
