Mail

Mail is a system, a service or a vehicle of trasmission of written documents.
The use of mail is very ancient, and perhaps its origin is deeply related to the invention of writing, as a means to transmit informations.
The first use as a service for the transmission of documents was perhaps in China, probably around 4000 BC. It is known that in Egypt, Pharaons used couriers for the diffusion of their decrees in the territory of the State (2400 BC). In the Old Testament too (Esther, VIII), there is a mention of Assuero, king of Medii, using couriers for communicating his decisions.
Xenophon attributes the invention to Cyrus the Great, while other writers indicated his successor Darius. The service was (later) called angariae, a term that in time turned to indicate a tax system.
It was in ancient Rome that a true mail service was organised, at the time of Augustus. The service was called cursus publicus, and was provided with light carriages called rhedae with fast horses; additionally there was another service, slower than the other one, managed with two-wheels cars (birolae) pulled by oxen. This service was reserved to the government's correspondence, another service for citizens was later added.
By the name of the stations in which mail was distributed and messengers' routes crossed, derives the latin name of mail, Posta (originally posata or pausata = place of rest) because in these stations messengers used to rest during their voyages. The english term "mail" is instead supposed coming from the Teutonic name for the bag used by messengers.
Another important postal service was created in the Islamic world by the caliph Moàvia; the service was called berid, by the name of the towers that were built in order to protect the roads by which couriers travelled.
Well before the Middle Ages and during them, carrier-pigeons were used, taking advantage of a singular quality of this bird, that when brought far from its nest is able to find his way home due to a particularly developed sense of orientation. Messages were then tied around the legs of the pigeon that was freed and could reach his original nest, where the receiver was.
Charlemagne extended to the whole territory of his empire the system used by Franks in northern Gaul, and connected this service with the service of missi dominici.
Many Holy Orders had a private mail service, notably Cistercians's one connected more than 6,000 abbeys, monasteries and churches. The best organisation however was created by Teutonic Knights. The newly insitituted universities too had their private services, starting from Bologna (1158)
Before that popular illiteracy was fought (mainly in 20th century and particularly in western countries), illiterates who needed to communicate dictated their messages to a scribe, another profession now quite generally disappeared.
Modern mail is usually organised by national services (that in recent times are increasingly being replaced by private owned companies), reciprocally interconnected by international regulations (some of which still in their original form of 18th century), organisations and agreements.
Usually the payment for the service is settled with the sticking of a pre-paid for stamp; stamp is then annuled by the postal officer. Stamps are also object of a particular form of collectionism called phylately, and often their commercial value on this specific market becomes enormously greater that the printed one, even after use. Another form of collectionism regards post cards, a document written on a single robust sheet of paper, usually decorated with photographic pictures or artistic drawings on one of the sides, and short messages on a small part of the other side, that also contained the space for the address. The fact that this communication is visible by other than the receiver, often causes the messages to be written in jargons.
Mail is quite generally protected by the secret of correspondance (secretus epistulae), meaning that no letter or other document can be read by other than the receiver. Usually special procedures are required in case correspondance has to be, openly or discreetly, controlled by police. The operations of control of the private citizens' mail is called censorship and concerns social, political, legal aspects of the civil rights. 
The use of mail is subject to common rules and a particular etiquette. After the discovery of new communicating systems and vehicles, mail lost most of its special charme in favour of more quick connecting systems such as the telephone, and remained as a vehicle for commercial or formal documents. It is however still widely in use in more cultivated classes for personal communication.
In modern times, mainly in 20th century, mail has found an evolution in vehicles using newer technologies to deliver the documents, especially through the telephone nets; these new vehicles include telegram, telex, fac-simile (fax), e-mail, short-message-service (sms). These vehicles commonly use a mechanic or electro-mechanic standardised writing (typing), that on one side effectively helps for an easier communication, while on the other side rendered quite obsolete the ancient art of calligraphy.
The ordinary mail service was improved with the use of planes for a quicker delivery (air mail) and receipts services were made available in order to grant the sender a conformation of effective delivery. Also, a general system of codes was created (zip codes), in order to make more operations managed by authomatical instruments.
 
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::Examples of famous letters...