Place the books in separate boxes and write the address of the recipient legibly on the inside and the outside of the boxes. Each book needs to be put in a separate box even if the books are going to the same destination.
Close the boxes and seal them.
Bring the boxes to the post office and ask for a U.S. Postal Service M-bag. This is a canvas duffel bag or sack where all the boxes are placed. The M-bag must weigh less than 66 pounds.
M-bags can be Airmail M-bags, International Priority Airmail M-bags, and International Surface Air Lift M-bags. They are specifically made for sending printed matter by air or surface mail.