MPO

MPO - see Mobile Post Office.
MPP - see Mailer's Permit Postmark.
Mr. ZIP - a cartoon-like character used as a marginal marking from 1964 to 1986 promoting the use of ZIP Code.

MPO: Mobile Post Office. Portable mail-handling equipment and personnel, generally in railroad cars, streetcars, trucks or buses.

military post office (MPO)—A branch of a U.S. civil post office operated by the Army, Navy, Air Force, or Marine Corps to serve military personnel overseas or aboard ships. Also see army post office (APO) and fleet post office (FPO).

See also: Stamp, Used, Cancel, Cover, Local