Postal authorities often have functions other than transporting letters. In some countries, a postal, telegraph and telephone (PTT) service oversees the postal system, in addition to telephone and telegraph systems. Some countries' postal systems allow for savings accounts and handle applications for passports.
The Universal Postal Union (UPU), established in 1874, includes 192 member countries and sets the rules for international mail exchanges.
The word mail comes from the Medieval English word male, referring to a travelling bag or pack. It was spelled that way until the 17th century, and is distinct from the word male. The French have a similar word, malle for a trunk or large box, and mla is the Irish term for a bag. In the 17th century, the word mail began to appear as a reference for a bag that contained letters: "bag full of letter" (1654). Over the next hundred years the word mail began to be applied strictly to the letters themselves, and the sack as the mailbag. In the 19th century the British usually referred to mail as being letters that were being sent abroad (i.e. on a ship), and post as letters that were for localized delivery; in the UK the Royal Mail delivers the post, while in the U.S. the U.S. Postal Service delivers the mail. The term email (short for "electronic mail") first appeared in the 1970s. The term snail-mail is a retronym to distinguish it from the quicker email. Various dates have been given for its first use.
Post is derived from Medieval French poste, which ultimately stems from the past participle of the Latin verb ponere ("to lay down or place").
The practice of communication by written documents carried by an intermediary from one person or place to another almost certainly dates back nearly to the invention of writing. However, development of formal postal systems occurred much later. The first documented use of an organized courier service for the diffusion of written documents is in Egypt, where Pharaohs used couriers for the diffusion of their decrees in the territory of the State (2400 BC). The earliest surviving piece of mail is also Egyptian, dating to 255 BC.
The first credible claim for the development of a real postal system comes from Ancient Persia, but the point of invention remains in question. The best documented claim (Xenophon) attributes the invention to the Persian King Cyrus the Great (550 BC), who mandated that every province in his kingdom would organize reception and delivery of post to each of its citizens. He also negotiated with neighbouring countries to do the same and had roads built from the city of Post in Western Iran all the way up to the city of Hakha in the East. Other writers credit his successor Darius I of Persia (521 BC). Other sources claim much earlier dates for an Assyrian postal system, with credit given to Hammurabi (1700 BC) and Sargon II (722 BC). Mail may not have been the primary mission of this postal service, however. The role of the system as an intelligence gathering apparatus is well documented, and the service was (later) called angariae, a term that in time came to indicate a tax system. The Old Testament (Esther, VIII) makes mention of this system: Ahasuerus, king of Medes, used couriers for communicating his decisions.
The Persian system worked on stations (called Chapar-Khaneh), where the message carrier (called Chapar) would ride to the next post, whereupon he would swap his horse with a fresh one, for maximum performance and delivery speed. Herodotus described the system in this way: "It is said that as many days as there are in the whole journey, so many are the men and horses that stand along the road, each horse and man at the interval of a day's journey; and these are stayed neither by snow nor rain nor heat nor darkness from accomplishing their appointed course with all speed". The verse prominently features on New York's James Farley Post Office, although it has been slightly rephrased to Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds.