An FPO and APO address is an address that people use for military or diplomatic shipments to prevent confusion with foreign mail networks. The United States Postal Services transfers shipments addressed to FPO to the Navy and routes those marked APO to the San Francisco military gateway.
The Department of Defense and the USPS established the Overseas Military Mail System to facilitate mail shipments to the U.S. Navy, military posts in foreign regions and U.S. Embassies worldwide. The system uses special addresses to ensure that shipments do not enter foreign mail networks. People who send mail to military or diplomatic posts must address it to the Army Post Office, or APO, the Fleet Post Office, or FPO, or the Diplomatic Post Office, or DPO. Senders must replace the city name with APO or FPO, state the routing region and use a special ZIP code. The routing region codes are AA for Armed Forces in the Americas, AE for Armed Forces in Europe and AP for Armed Forces in the Pacific.
Military shipments must have the full names, grade and unit number of the recipient. Shipments meant for the Navy must include the ship name or fleet number. The USPS assigns special ZIP codes to military bases and organizes them by country or region.