Only FedEx SmartPost, which uses the USPS system in the last leg of delivery, will deliver to domestic P.O. Boxes. Learn more about FedEx SmartPost.
FedEx Express can ship to a P.O. Box in some international destinations, including Puerto Rico, but you are required to provide a valid telephone, fax, or telex number.
All other FedEx services do not deliver to PO Boxes (or any sort of lockboxes) for addresses in the United States. If you are attempting to ship to a PO Box using a FedEx service that does not deliver to that address, you will see a warning in the app.
On the ORDERS page:
On the READY TO SHIP page: