How postal barcodes work and how to read them

In the 1980s, the United States Postal Service (USPS) faced the challenge of handling an ever-climbing number of mail items, which had more than tripled since WWII. It urgently sought a technological solution to decrease the manual labor involved in processing these, similar to what letter sorting machines had achieved in the 1960s.

At the same time, the Universal Product Code (UPC) had already found its footing in American supermarkets, enabling cashiers to check out items at an unprecedented speed. The USPS had already experimented with early barcode versions to make ZIP codes machine-readable. However, to facilitate processing even further, it needed something as powerful as the UPC.

POSTNET, PLANET, and Intelligent Mail barcodes

The result was the Postal Numeric Encoding Technique, or POSTNET for short. This barcode symbology uses groups of five half- and full-length bars to encode the recipient’s ZIP code, facilitating the automated sorting and processing of mail.

Some years later, POSTNET was complemented by the PLANET (Postal Alpha Numeric Encoding Technique) barcode. It uses the same 2-state code symbology to encode information for tracking and confirmation of delivery.

In the mid-2000s, the USPS combined the features of POSTNET and PLANET into a more advanced postal barcode with higher data density: the Intelligent Mail barcode (IMb). It fully replaced both POSTNET and PLANET in 2013.

The IMb belongs to the category of 4-State Customer Codes, which are now used by postal services worldwide. Instead of bars that are either half- or full-length, they use bars made up of three regions (called “tracking”, “ascending”, and “descending”) that combine to form four possible states.

The Intelligent Mail symbology encodes a barcode identifier, a service type identifier, a mailer ID, a serial number, and typically a routing code (ZIP code). It also features built-in error detection, but no automatic error correction.

What makes postal barcodes unique

Many postal services use a 4-State Customer Code symbology to route and track mail, including the UK’s Royal Mail, the Dutch PostNL, Australia Post, and Japan Post.

They are quite distinct from other symbologies, however: Unlike regular 1D barcodes, it is not the width but the height and position of the bars in a 4-State Customer Code that encodes information. Traditional laser scanners cannot read them, which is why postal barcodes are sometimes regarded as a separate category.

Some postal barcodes, however, do use regular 1D symbologies: The German postal service Deutsche Post and its logistics division DHL use two variations of the Interleaved 2 of 5 (ITF) barcode. Called “Identcode” and “Leitcode”, they hold details about fulfillment and an item’s destination, respectively. Deutsche Post and DHL also make heavy use of 2D barcodes, specifically Data Matrix codes.

Postal 2D barcodes

Two-dimensional barcodes can store a lot more data than their 1D counterparts. Therefore, postal services commonly use 2D codes to provide additional tracking metrics to commercial and private customers. Examples include the Royal Mail Mailmark and the Data Matrix codes on Deutsche Post stamps, which even have built-in anti-counterfeiting measures.

Another advantage of a 2D barcode is its high error tolerance: Even if parts of the code are damaged or obscured, it might still be possible to scan it correctly. Depending on the symbology, up to 30% of the code can be destroyed and still be readable. This makes two-dimensional barcodes a reliable tool for tracking items over long distances and across multiple touchpoints.

Choosing the right postal barcode scanner

Barcode scanners have traditionally been dedicated devices, whether stationary or handheld. Today, however, these specialized tools are being replaced by mobile scanning apps, thanks to the high-resolution cameras and powerful processors of today’s smartphones.

Using a software development kit (SDK), you can even integrate barcode scanning features into existing apps – there is no need to develop a solution from scratch.

The Scanbot Barcode Scanner SDK for iOS, Android, Windows, and Web is available for all common development frameworks, including Flutter, React Native, Xamarin, and .NET MAUI. By integrating it into your application, you can turn your smartphones and tablets into reliable, easy-to-use mobile scanning devices in a matter of hours. Built with machine learning technology, the SDK delivers fast and accurate scanning results, even without an internet connection: All processing happens on the device itself.