How USPS Tracking Works: The Tech Behind It

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United States Postal Service (USPS) tracking is a record of scans of an item’s label, not a live reading of where a package is. The record can begin when the sender notifies USPS to expect the item, and it continues through acceptance and delivery or pickup.

That record can have gaps or be wrong. A package can arrive with no delivery scan, USPS says. In a 2023 inspector general audit, the messages for 318 of 500 packages did not match the place, time or date the auditors observed. The auditors chose those packages rather than sampling at random, so the share does not describe all USPS packages. A gap in updates is a reason to check the message and its timing before treating the item as lost.

The barcode identifies the package and guides its route

The Intelligent Mail package barcode (IMpb) is a USPS-developed barcode that automated equipment and scanning devices can read. Its data generally follows the GS1-128 barcode standard and supplies tracking and routing information. The barcode identifies the package and tells equipment how to handle it; it does not measure where the package is.

USPS requires each package to bear a unique IMpb, and its routing information lets automated equipment sort and track packages to their delivery post offices. The barcode’s fields cover the destination ZIP Code, a package identification code, the mailer’s identity and the combination of mail class and services. It also includes a serial number for the package. These fields solve different problems: the destination directs the journey, while the identifier keeps records for separate packages from being confused.

USPS standards also describe the Intelligent Mail matrix barcode (IMmb), a supplemental two-dimensional barcode that carries the same data as the IMpb in a more compact format and is intended to improve package visibility.

To get USPS’s commercial base prices, commercial packages must have an IMpb and come with an electronic file that includes the required address information. The tracking record draws on files like that as well as on scans.

Tracking still depends on a label that a machine or employee can scan. USPS’s mailing standards say ordinary white label stock is generally suitable for barcodes if it is neither glossy nor prone to smearing or smudging. Place the label on the longest side of the box, keep it from wrapping around an edge and make sure the barcode faces up, USPS advises.

How a scan becomes an update

Product Tracking and Reporting (PTR) is the USPS database that stores tracking scans for barcoded packages and products with extra services. Its information comes from business mailers’ files, handheld scanners, retail equipment, mail-processing equipment and other postal systems.

A 2017 audit by the USPS Office of Inspector General described carriers using a handheld Mobile Delivery Device (MDD) to scan packages and transmit tracking data through a cellular network, with Global Positioning System (GPS) technology supplying location information. That is the location of the carrier’s device when it scans, not a continuous reading of where the package is.

A delivery unit is a postal facility with mail-delivery functions, such as a Post Office, station, branch or carrier annex. That audit used GPS information to identify improper scans, those made at a postal delivery unit instead of at the delivery location. It found about 1.9 million of them, 7 percent of the 25.5 million scans it analyzed that way. Where a scan happens matters as much as the status selected, because a delivery scan should match an actual delivery attempt.

The same equipment and scan data are used to check postage. USPS processing equipment can detect postage discrepancies when the weight or dimensions entered for an online label differ from the package’s actual characteristics. For commercial mailers, the USPS Ship platform compares submitted package documentation with physical attributes from scan data to determine postage and provides reports and data feeds.

USPS says scanning information is updated throughout the day as scans become available. PTR supplies tracking-event files to business customers, while individual customers can check delivery status on the USPS Tracking website and request proof of delivery or email notification when applicable. A tracking page with no new updates can mean the package is waiting, moving or missing a scan.

A tracking status can describe a prediction

An inspector general audit issued May 11, 2023, examined tracking messages for 500 packages selected by auditors rather than chosen randomly, from 25 states. It found that messages for 318 did not accurately reflect the location, time or date observed by auditors. Those findings describe the audit’s selected packages, not a national error rate for today’s shipments.

The auditors traced the problems to a combination of factors, including missing package scans, which can happen when a barcode is unreadable or a required scan is not completed, and programming that reported a package’s expected movement rather than its actual location. They found that messages such as “Out for Delivery” or “In Transit” could appear while a package was still at a facility.

USPS’s Expected Delivery Window is a two-hour estimate; delivery within it is not guaranteed, and a package that misses it may still arrive by the end of the day. USPS Tracking itself does not speed up or guarantee delivery.

Packages may arrive with a different carrier and at a different time from the regular mail. An empty mailbox after the regular mail arrives does not mean that day’s package deliveries are finished.

Letters and Informed Delivery use different visibility

USPS Ground Advantage, Priority Mail and Priority Mail Express all include USPS Tracking. Prepaid Forever Priority Mail Flat Rate products are excluded from Priority Mail’s included tracking. Tracking adds no separate charge to products that automatically include it, while adding tracking to commercial USPS Marketing Mail parcels requires a fee.

Ordinary First-Class Mail postcards, letters and flats are not eligible for USPS Tracking, although extra services such as Certified Mail and Registered Mail provide barcode-based tracking. USPS uses the word “flats” for large envelopes, newsletters and magazines. For letters and flats, the Intelligent Mail barcode (IMb) is a 65-bar code used to sort and track mail. A barcode on a letter does not mean the recipient gets the tracking a package gets.

Informed Visibility Mail Tracking & Reporting (IV-MTR), an application for the mailing industry, provides near-real-time tracking information for letters and flats. Some events in that system are inferred: it includes assumed handling events and logical delivery events based on business rules. Neither is proof that someone scanned that letter at a front door.

Informed Delivery is the free USPS service that shows preview images of incoming mail and status updates for incoming and outgoing packages. USPS cautions that the images show letter-sized mail processed through automated equipment and that the pictured mail may take several days to arrive.

Match the next step to the message

Contact the shipper with questions when a label has been created but USPS is still awaiting the item. If an Out for Delivery package has not arrived after one full postal business day following the scan, submit a service request to the local post office using its tracking number.

A No Access to Delivery Location message means the carrier could not reach the delivery spot, potentially because of a blocked mailbox, animal interference or a locked building. USPS says it will automatically retry the next business day; check for obstructions and submit a service request if more than 24 hours have passed since that status.

A Notice Left (No Authorized Recipient Available) message instead means the item requires a signature and no one was available to sign. There is no automatic second attempt for that status: schedule redelivery or arrange pickup from the post office listed on the notice, with valid photo identification.

For an item marked delivered but not located, check with household members and look around the mailbox, porch, garage, protected areas and exterior doors, USPS advises. If an eligible item still cannot be found more than one postal business day after the delivered scan, use USPS’s Email Us page to submit a service request to the local post office. For an item received without a delivery scan, USPS recommends confirming delivery with the sender or recipient.

A Missing Mail search request can be submitted starting seven days from mailing. The request needs sender and recipient addresses, container details, identifying information such as the tracking number and mailing date, a description of the contents and helpful pictures.

USPS warns that it sometimes cannot find missing mail, and that an item may not be recovered because it was not safe to forward. Separately, a refund may be available for a service with a money-back guarantee, such as Priority Mail Express, and an insurance claim for mail that included insurance. For Priority Mail Express items to or from Alaska and Hawaii, USPS stopped processing guarantee refund requests as of August 1, 2023, though it still processes refund requests for loss. For lost domestic insured mail, the claim window is 15 to 60 days after mailing; Priority Mail Express starts at 7 days, while military-mail services have different windows. For insured mail with damaged or missing contents, USPS recommends filing a claim immediately and requires filing no later than 60 days from mailing. Waiting for a search result can use time needed to file a claim.

Keep the mailing receipt or retained label portion: USPS says it cannot locate an item without the tracking number. Use the USPS Tracking website, the USPS Mobile app or the phone options listed by USPS to check updates. For text tracking, send the number to 28777 for the latest information; standard message and data rates may apply.