POSTNET vs Intelligent Mail Barcode: Transition, Differences, and Current Alternatives

Introduction

Postal barcode standards have evolved from the numeric-only POSTNET to the richer Intelligent Mail Barcode (IMb). For anyone learning about mail automation, understanding the differences, reasons for transition, and current alternatives is important—especially for businesses, fulfillment centers, and shipping software developers who must comply with postal requirements. This article explains the technical differences, practical implications, migration considerations, and modern alternatives to POSTNET.

Technical Differences: POSTNET vs IMb

POSTNET (Postal Numeric Encoding Technique) encoded only digits related to the delivery address: ZIP, ZIP+4, and sometimes a delivery-point code. Its representation used tall and short bars in fixed five-bar patterns per digit and required a check digit for error detection.

Intelligent Mail Barcode is a more advanced symbology that encodes up to 31 digits of information in a single barcode made up of four-state vertical bars. IMb supports:

• Routing and location information (like POSTNET)
• Mailing and class information (e.g., permit and service types)
• Tracking and service events—IMb can carry a tracking code enabling end-to-end visibility within USPS networks
• Higher data density in the same physical space—fewer physical constraints for larger information payloads

In short, IMb consolidates and expands what POSTNET and other older barcodes (like PLANET) did separately. IMb’s four-state design makes it possible to pack substantially more information in a single barcode area while improving postal services like tracking.

Why USPS Replaced POSTNET

The USPS wanted a single, unified barcode that could support automation, tracking, and additional services without requiring multiple codes on the same mail piece. IMb simplified processing, reduced the need for separate barcodes, and enabled modern tracking services that customers expect today. Over time the USPS phased out the requirement for POSTNET-based automation discounts and encouraged migration to IMb for improved operational efficiency.

Practical Implications of the Transition

For mailers, the transition meant updating mailing software, printers, and processes. Key changes included:

• Software updates: Address hygiene tools and postage software had to support IMb generation and validation.
• Printer and ink considerations: IMb’s four-state bars impose different print quality demands; printers needed to be able to render the denser barcode accurately.
• Data management: IMb requires or benefits from richer datasets (more identifiers and service codes) than POSTNET, so CRMs and order systems sometimes needed changes.

Migration Tips

• Inventory your systems and suppliers—know which platforms produce POSTNET and which support IMb.
• Update address verification tools to append required IMb data fields and to validate barcode placement and print quality.
• Run parallel testing—produce sample runs with IMb and confirm postal acceptance and any new discounts or service capabilities.
• Train staff and document processes so production, quality control, and returns teams understand the new barcode’s handling.

Alternatives and Complementary Technologies

Beyond IMb, other technologies have emerged in shipping and logistics that serve purposes POSTNET never could:

• 2D barcodes (QR codes, Data Matrix): Useful for encoding large amounts of data such as product SKUs, URLs, or batch information. Not a USPS standard for routing but excellent for internal operations or on-package consumer interactions.
• RFID: Radio-frequency identification can support high-speed sorting and tracking in some logistics operations but requires different infrastructure and cost models.
• Cloud-based tracking and APIs: Modern TMS and shipping platforms use cloud APIs to share tracking data between carriers and shippers, complementing on-package barcodes.

When POSTNET Might Still Appear

You may still encounter POSTNET in legacy mailings, historical archives, or older automated equipment. Philatelists, postal historians, and organizations processing older files or archives should be able to recognize POSTNET. If you operate older in-house printing equipment that only outputs POSTNET, consider upgrading to support IMb to qualify for current discounts and tracking services.

Choosing the Right Approach Today

For most mailers, IMb is the correct standard because it enables tracking and carries more data needed by modern postal systems. If you manage transactional or marketing mail at scale, migrate to IMb-capable software and printers. For logistics or package labeling where more data is needed or consumer interaction is intended, pair IMb with 2D codes or use QR codes for additional content and APIs for real-time tracking.

Conclusion

POSTNET was foundational for automated mail routing, but the Intelligent Mail Barcode replaced it to meet the needs of modern postal operations—tracking, richer data, and unified processing. Understanding their differences helps organizations plan migrations, choose compatible technologies, and ensure mailings meet postal requirements while enabling more sophisticated tracking and service features. For anyone working in mailing, shipping, or fulfillment, the lesson is to favor current standards (IMb and compatible systems) while recognizing POSTNET’s role in the evolution of postal automation.