12-28-2021 10:58 PM
12-29-2021 01:32 AM
Yes, if they don't have advertising. Here's a chart that USPS put together for staff reference:
https://liteblue.usps.gov/news/link/2013/04apr/Media-Mail-Guidelines.htm
12-31-2021 08:29 PM
Yes, as long as only advertizing contained is incidental adverts of other books.