Media rate is a very cheap way to send books. Originally it was called 'book rate'. With the advent of records, cd's, dvd's and computers; it's had a name change and new specifications.
It's 1 of only 2 types of mail that can be opened by ANYBODY during handling. [to insure it's the correct items inside. Others can only be opend by postal inspectors. Just like customs officers can open items coming into the country.]
IF it's found to not be mailable material, it then will be returned to the sender. The sender will then have to repackage the item
from here:
http://pe.usps.com/text/dmm300/473.htm#1015188
3.0 Content Standards for Media Mail Parcels
3.1 Basic Content Standards
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.
b. 16-millimeter or narrower width films, which must be positive prints in final form for viewing, and catalogs of such films of 24 pages or more (at least 22 of which are printed). Films and film catalogs sent to or from commercial theaters do not qualify for the Media Mail price.
c. Printed music, in bound or sheet form.
d. Printed objective test materials and their accessories used by or on behalf of educational institutions to test ability, aptitude, achievement, interests, and other mental and personal qualities with or without answers, test scores, or identifying information recorded thereon in writing or by mark.
e. Sound recordings, including incidental announcements of recordings and guides or scripts prepared solely for use with such recordings. Video recordings and player piano rolls are classified as sound recordings.
f. Playscripts and manuscripts for books, periodicals, and music.
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.
h. Loose-leaf pages and their binders consisting of medical information for distribution to doctors, hospitals, medical schools, and medical students.
i. Computer-readable media containing prerecorded information and guides or scripts prepared solely for use with such media.
3.2 Enclosures in Books
Enclosures in books mailed at Media Mail prices are subject to these additional standards:
a. Either one envelope or one addressed postcard may be bound into the pages of a book. If also serving as an order form, the envelope or card may be in addition to the order form permitted by 3.2b..
b. One order form may be bound into the pages of a book. If also serving as an envelope or postcard, the order form may be in addition to the envelope or card permitted by 3.2a..
c. Announcements of books may appear as book pages. These announcements must be incidental and exclusively devoted to books, without extraneous advertising of book-related or other materials or services. Announcements may fully describe the conditions and methods of ordering books and may contain ordering instructions for use with a separate order form. Up to three such announcements may contain as part of their format a single order form. The order forms permitted with these announcements are in addition to order forms that may be enclosed under 3.2a. or 3.2b..
Note this part:
" 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. "
That's what stops codexes. Also why you can't send White Dwarf as media rate.
and this part:
" 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".
That's what stops game boxes. They're not books but games, the same as Monopoly or Risk.
Like I said, Player's Handbook, DM guides and such, usually yes. [unless it has alot of ads.] Modules, adventures, scenarios, probably no. [if it has an isbn and no ads.] Box sets with maps definately no.
Is it like a novel or dictionary, then yes. Is it like a board game, like Risk or Sttlers of catan; then no.
