For those who are selling back issues of magazines should check with the USPS to find out what the latest rules and regulations are on shipping magazines "Media Mail". From experience, I learned that magazines can not be shipped Media, because they have Advertising articles in them. Magazines can only be shipped First Class, Parcel Post or Priority Mail or Internation form of shipment.
USPS Customer's Guide to Mailing:
MEDIA MAIL (tm) - Small and large packages and thick envelopes can be sent using Media Mail. Contents are limited to books, manuscripts, sound recordings, recorded videotapes, and computer-readable media (not blank). Informally called "Book Rate," Media Mail cannot contain advertising, except eligable may contain incidental announcements of books. Media Mail is usually less expensive than Parcel Post.