Postmarking

Postmarking refers to the act of applying a postmark to mail items by a postal authority. The postmark typically indicates the date and origin of mailing and serves to cancel the postage stamp so it cannot be reused. The practice is a core function of postal systems and helps document the mailing timeline and routing of items.

Postmarks come in several forms. Common types include circular date stamps (CDS) that show date and location, wavy-line or bar-style cancellations, and straight-line cancels. Many postal operators also employ machine cancellations that combine date information with facility identifiers. Some marks may include the time of day, a postal facility code, or commemorative imagery for special events.

Purposes and uses of postmarking include authentication of when a letter was posted, aiding postage-rate calculations and mail tracking, and preventing stamp reuse. In philately, postmarks are of particular interest to collectors, who seek clear, well-centered dates and distinctive postmarks from rare or historical post offices.

Standards and variation: Postmark design and application vary by country and operator. International guidelines are influenced by the Universal Postal Union, which promotes legibility, consistency, and traceability, while national differences reflect local practices and equipment. Modern systems increasingly rely on electronic or computer-generated marks for efficiency, while physical postmarks remain essential for many types of mail.

Related concepts: The terms “postmark” and “cancel” are related but not identical; a postmark dates and authenticates, while a cancellation physically marks the stamp to deter reuse. In digital contexts, electronic postmarks provide time-stamped evidence for electronic documents and communications.