The UPU S10 Standard is a pivotal guideline established by the Universal Postal Union (UPU), a specialized agency of the United Nations, which streamlines international postal tracking systems for member countries. This standard stipulates the necessary structure for postal tracking numbers, ensuring they are universally recognized and efficiently processed across international postal services. The standard format, denoted as XX123456789YY, consists of two letters, followed by nine digits, and concludes with two additional letters, commonly referred to as the "A2-N9-A2" format.

In addition to defining formats, the UPU S10 outlines service indicators, serial numbers, check digits, and country codes, facilitating accurate tracking of various postal products. The UPU S10 identifiers are managed by designated organizations within member countries, such as USPS in the USA and China Post in China, promoting consistent usage.

For end-users, a free online validator is available, enabling quick verification of tracking numbers, thereby enhancing the reliability of postal services and ensuring confidence in package deliveries for both consumers and businesses alike.