A postmark is a postal marking made on a letter, package, postcard or the like indicating the date and time that the item was delivered into the care of the postal service. Modern postmarks are often applied simultaneously with the cancellation or killer that marks the postage stamp(s) as having been used (though in some circumstances there may be a postmark without a killer, and sometimes the postmark and killer form a continuous design), and the two terms are often used interchangeably, if incorrectly. Postmarks may be applied by hand or by machines, using methods such as rollers or inkjets, while digital postmarks are a recent innovation. The local post Hawai'i Post had a rubber-stamp postmark parts of which were hand-painted. At Hideaway Island, Vanuatu, the Underwater Post Office has an embossed postmark.
The General Post Office in St. Martin's Le Grand (later known as GPO East) was the main post office for London between 1829 and 1912, the headquarters of the General Post Office of the United Kingdom of Great Britain and Ireland, and the country's first purpose-built post office.