Yes, you can return books by mail. We recommend that you insure them in case of damage or loss.
Send them to: Van Pelt Library Circulation 3420 Walnut St. Philadelphia, PA 19104-6206.
Books from any Penn library may be returned to Van Pelt. If you are unable to renew books online through your Franklin account, you may also contact the Van Pelt Library circulation desk for help. They may be reached at: (215) 898- 7566 or vpcircdk@pobox.upenn.edu
Note that this is different from the Books-by-Mail program.