A mail plane is an aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 used for carrying mail

Mail

Mail, or post, is a system for transporting letters and other tangible objects: written documents, typically enclosed in envelopes, and also small packages are delivered to destinations around the world. Anything sent through the postal system is called mail or post.In principle, a postal service...

.

Aircraft that were purely mail planes existed almost exclusively prior to World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. Because early aircraft were too underpowered to carry cargoes, and too costly to run any "economy class" passenger-carrying service, the main civilian role for aircraft was to carry letters faster than previously possible. In 1934, some mail services in the USA were operated by the United States Army Air Corps

United States Army Air Corps

The United States Army Air Corps was a forerunner of the United States Air Force. Renamed from the Air Service on 2 July 1926, it was part of the United States Army and the predecessor of the United States Army Air Forces , established in 1941...

, soon ending in the Air Mail scandal

Air Mail Scandal

The Air Mail scandal, also known as the Air Mail fiasco, is the name that the American press gave to the political scandal resulting from a congressional investigation of a 1930 meeting , between Postmaster General Walter Folger Brown and the executives of the top airlines, and to the disastrous...

.

In the past, mail-carrying aircraft had to carry a special official emblem on the fuselages; in case of British-registered aircraft, a special Royal Air Mail pennant (a blue triangular flag with a crowned bugle

Bugle (instrument)

The bugle is one of the simplest brass instruments, having no valves or other pitch-altering devices. All pitch control is done by varying the player's embouchure, since the bugle has no other mechanism for controlling pitch. Consequently, the bugle is limited to notes within the harmonic series...

 emblem in yellow and the letters "ROYAL AIR MAIL" in white) would sometimes be flown as well.

From the late 1940s, mail planes became increasingly rare, as the increasing size of aircraft and economics dictated a move towards bulk carriage of mail onboard airline

Airline

An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...

 flights, and this remains the primary method today. Parcel mail, overnight mail and priority mail, however, are still carried aboard what may be considered the spiritual successors of classic, pre-war mail planes; small, general aviation

General aviation

General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...

 aircraft that have been adapted to the role, with the Cessna 208

Cessna 208

The Cessna 208 Caravan is a single turboprop engine, fixed-gear short-haul regional airliner and utility aircraft built in the United States by Cessna. The airplane typically seats nine passengers, with a single person crew, although with a FAR Part 23 waiver, it can seat up to fourteen passengers...

 and Piper PA-31 Navajo

Piper PA-31 Navajo

The Piper PA-31 Navajo is a family of cabin-class, twin-engine aircraft designed and built by Piper Aircraft for the general aviation market, most using Lycoming engines. It was also licence-built in a number of Latin American countries. Targeted at small-scale cargo and feeder liner operations and...

 being among the most popular. Cargo airline

Cargo airline

Cargo airlines are airlines dedicated to the transport of cargo. Some cargo airlines are divisions or subsidiaries of larger passenger airlines.-Logistics:...

 operators, such as UPS

United Parcel Service

United Parcel Service, Inc. , typically referred to by the acronym UPS, is a package delivery company. Headquartered in Sandy Springs, Georgia, United States, UPS delivers more than 15 million packages a day to 6.1 million customers in more than 220 countries and territories around the...

 and FedEx

FedEx

FedEx Corporation , originally known as FDX Corporation, is a logistics services company, based in the United States with headquarters in Memphis, Tennessee...

, also carry mail along with bulk cargo, aboard converted airliners.