Universal Postal Union in the context of "Republic of China (1912–1949)"

A postal code (also known locally in various English-speaking countries throughout the world as a postcode, post code, PIN or ZIP Code) is a series of letters or digits or both, sometimes including spaces or punctuation, included in a postal address for the purpose of sorting mail.

As of August 2021, the Universal Postal Union lists 160 countries which require the use of a postal code.

The Hellenic Post S.A. (Greek: Ελληνικά Ταχυδρομεία, abbreviated ΕΛΤΑ, ELTA) is the state-owned provider of postal services in Greece. It succeeded the former government Postal Service, founded in 1828. ELTA provides a universal postal service to all parts of Greece and is a member of the Universal Postal Union. Services provided include: letter post; parcel service; deposit accounts; Swiftpost, a nationwide next-day delivery service; and the EMS international express mail service.

The Treaty of Bern (formally the Treaty concerning the formation of a General Postal Union), signed on 9 October 1874, established the General Postal Union, which is today known as the Universal Postal Union. Named for the Swiss city of Bern, where it was signed, the treaty was the result of an international conference convened by the Swiss Government on 15 September 1874. It was attended by representatives of 22 nations. Plans for the conference had been drawn up by Heinrich von Stephan, Postmaster-General of the German Reichspost who demanded from the neutral Switzerland the organization of an International Postal Congress following the end of the French-German war of 1870–1871.

The purpose of the treaty was to unify disparate postal services and regulations so that international mail could be exchanged freely. The signatories of the treaty were the German Empire, Austria-Hungary, Belgium, Denmark, Egypt, Spain, the United States, France, Great Britain, Greece, Italy, Luxembourg, the Netherlands, Portugal, Romania, the Russian Empire, Serbia, the United Kingdoms of Sweden and Norway, Switzerland, and the Ottoman Empire.

Airmail (or air mail) is a mail transport service branded and sold on the basis of at least one leg of its journey being by air. Airmail items typically arrive more quickly than surface mail, and usually cost more to send. Airmail may be the only option for sending mail to some destinations, such as overseas, if the mail cannot wait the time it would take to arrive by ship, sometimes weeks. The Universal Postal Union adopted comprehensive rules for airmail at its 1929 Postal Union Congress in London. Since the official language of the Universal Postal Union is French, airmail items worldwide are often marked Par avion, literally: "by airplane".

For about the first half century of its existence, transportation of mail via aircraft was usually categorized and sold as a separate service (airmail) from surface mail. Today it is often the case that mail service is categorized and sold according to transit time alone, with mode of transport (land, sea, air) being decided on the back end in dynamic intermodal combinations. Thus even "regular" mail may make part of its journey on an aircraft. Such "air-speeded" mail is different from nominal airmail in its branding, price, and priority of service.