Library Mail is an inexpensive way for libraries, academic institutions, museums, nonprofits, and similar organizations to send items on loan to one another. These groups can mail books, sound recordings, and other academic media, for the low rate of $2.59 for the first pound, and an additional $0.48 for each additional pound up to 70 pounds per shipment.
Senders must show a return address or address of a school or nonprofit organization. Some publishers can send items through Library Mail as long as they are being sent to a qualified recipient. Library Mail cannot contain advertising or other non-media materials except for a packing slip. Items take 7 to 10 days to arrive to their final destination.
The USPS will allow extra services for Library Mail, including insurance, USPS Tracking, Signature Confirmation, COD, return receipt and restricted delivery. A certificate of mailing, which provides proof of shipment, and special handling for fragile items, is also available.
Our mail room tell me this works out to about a nickel an ounce.