A postal service tracking number, also known as a shipment tracking number, is an identifier assigned to a mailpiece or parcel that allows the sender and recipient to track its progress through the postal system. For instance, the United States Postal Service (USPS) provides tracking numbers for registered mail, priority mail, and express mail. These numbers typically start with two letters, followed by nine digits, and end with two more letters.
Tracking numbers are important because they provide visibility into the whereabouts of a shipment, allowing the sender and recipient to estimate its delivery time and take necessary actions if there are any delays or problems. This feature is particularly useful for valuable or time-sensitive items. Historically, tracking numbers were manually assigned to each shipment, but the automation of postal systems has made it possible to generate and assign tracking numbers electronically, greatly improving efficiency and accuracy.