A
postal marking is any kind of annotation applied to a
letter by a postal service. The most common types are
postmarks and
cancellations; almost every letter will have those. Less common types include forwarding addresses, routing annotations, warnings,
postage due notices and explanations, such as for damaged or delayed mail and censored or inspected mail. A key part of
postal history is the identification of postal markings, their purpose, and period of use.