postmark

A postmark is an official mark placed on mail by a postal authority to indicate the date and place of mailing and to cancel the stamp so it cannot be reused. In postal systems, postmarks serve as a record of processing and help track delivery, routing, and eligibility for postage refunds or claims.

Historically, postmarks emerged in the 19th century with the expansion of organized postal services. They can take various forms, including circular date stamps that show city or town, date, and sometimes time, and machine cancellations that apply wavy lines or other patterns over the stamp. Some postmarks include additional information such as route codes or branch identifiers.

Postmarks are important to collectors in philately, where the design, legibility, and rarity of marks influence value. In everyday mail, postmarks verify when a letter was mailed and help determine deadlines for mail service promises. Some jurisdictions distinguish between postmarks and other types of postal markings, such as meter marks or handstamps used for canceling stamps.

In the modern postal environment, digital and automated processing has blurred distinctions, but most countries maintain official postmarks to preserve a verifiable date stamp. Some pieces of mail may lack a legible postmark if the stamp is prepaid or if processing equipment does not apply one.

Postmark is also the name of a cloud-based email delivery service owned by Wildbit. Launched to focus on transactional email, Postmark provides an API and SMTP interface, inbound parsing, templates, and analytics. It is marketed as a reliable option for developers requiring fast delivery and clear reporting.