How to Read an Intelligent Mail Barcode

Every piece of U.S. mail hides a chunk of data in the striped pattern printed in the address block. That pattern—called the Intelligent Mail® Barcode (IMb)—lets the United States Postal Service® (USPS) and mailers track, route, and verify billions of mailpieces every year. Mastering how to read an IMB unlocks actionable insights that improve delivery speed, lower postage costs, and keep your campaigns USPS‑compliant.

In this guide, we’ll walk you through each IMb component and show you why accurate decoding matters for marketers, mailers, and business owners alike.

What Is an Intelligent Mail Barcode?

The Intelligent Mail Barcode is a 65‑bar, four‑state (full, ascender, descender, tracker) barcode that consolidates the functions of several legacy USPS barcodes—POSTNET, PLANET, and ACS—into one powerful symbol. Encoded inside those bars are two data blocks:

Tracking Field: 20 digits uniquely identifying the mail owner, mail class, and individual piece.
Routing Field: 0–11 digits that carry the delivery ZIP Code™ for automated sorting.

Because every IMb is unique, USPS can scan a piece at each processing step, feed status updates back to the mail owner, and trigger informed‑delivery emails to recipients. Mailers like Presort embed IMBs on automation‑compatible mail—from postcards and letters to flats—so clients gain end‑to‑end visibility and qualify for the lowest automation postage rates.

Deciphering the Intelligent Mail Barcode

On the surface, the IMb looks like a random zebra pattern, but its 31 numeric digits follow a strict hierarchy. Understanding each layer is essential for accurate decoding.

IMB Tracking Code

The Tracking Code is the main aspect of the Intelligent Mail Barcode. It breaks down into four elements:

Barcode ID

2 digits that identify the presort level or service option.

Service Type ID

3 digits that indicate mail class (First‑Class‑Mail®, Marketing Mail®) and any ancillary services (Address Change Service, tracking, or signature).

Mailer ID

Either 6 or 9 digits assigned by USPS to the mail owner or service provider. A 6‑digit Mailer ID supports up to 9‑digit serial numbers; a 9‑digit Mailer ID supports 6‑digit serials.

Serial Number

9 or 6 digits uniquely identifying each mailpiece for up to 45 days, enabling piece‑level tracking.

At Presort, we generate Serial Numbers programmatically, ensuring zero duplication across millions of pieces, which is essential for clean data and accurate delivery analytics.

IMB Routing Code

The Routing Code represents the destination address in USPS sorting logic. Depending on your mailing list and presort depth, it can contain:

ZIP Code (5 digits)
ZIP+4 (9 digits)
Delivery Point Code (11 digits)

A fully populated 11‑digit Routing Code pushes the mailpiece deeper into USPS automation early in the process, shaving one to two days off average delivery times. Presort’s proprietary address‑quality software appends missing ZIP+4 and Delivery‑Point digits to give clients the fastest possible in‑home dates.

IMB Decoder: Translating Bars to Digits

Reading an IMB involves mapping every bar’s state to a binary value, grouping those bits into 13 five‑bit characters, and then converting each character to base‑10 digits using the USPS‑defined character table. While manual decoding is possible with a ruler and patience, Presort uses calibrated imaging scanners and USPS‑certified software to ensure error‑free reads at production speed.

Each of the 65 bars falls into one of four “states”:

Full Bar: Touches the top and bottom guardrails.
Ascender: Touches the top guardrail only.
Descender: Touches the bottom guardrail only.
Tracker: Falls between guardrails, touching neither.

Understanding these bar states is essential for accurate decoding, and with Presort’s advanced technology, you can rest easy knowing that every barcode is read with precision and reliability.

Service Type Code Lookup

Although the 3‑digit Service Type ID lives inside the Tracking Code, it deserves special attention. By decoding this optional field, marketers can instantly see whether a piece was mailed First‑Class, Marketing Mail, or Parcel Select—and whether extra services such as “Move Update,” “Address Change Service,” or “Return Receipt” are active. Presort builds Service Type analytics into our reporting dashboards, allowing clients to slice delivery data by mail class or service without touching raw IMB strings.

Ready to put your Intelligent Mail Barcode knowledge to work? Explore Presort’s expert direct mail services and ensure every mailpiece is tracked, targeted, and delivered with precision.

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Why Accurate IMB Readings Are Important

A single misread digit can corrupt tracking data, misroute mail, or trigger USPS compliance issues. Following the steps above and leveraging a reliable mailing partner like Presort ensures your IMb data is conveyed efficiently and safely. Some of the most important reasons to ensure your Intelligent Mail Barcodes are read accurately include the following:

Improved Mail Efficiency: Accurate barcodes speed pieces through automated sorters, reducing transit time and handling costs.
Real‑Time Tracking: Clean IMBs feed reliable scan data to USPS Informed Visibility®, letting you monitor delivery progress down to the individual piece.
USPS Compliance: Properly formatted IMBs satisfy Move Update and Full‑Service requirements, avoiding surcharges and penalties.
Better Campaign Timing: Precise delivery predictions enable perfectly timed follow‑up emails, calls, or digital ads that boost conversion rates.
Data‑Driven Decisions: Reliable scan events provide insights into drop‑to‑delivery performance, empowering you to refine future mail schedules and list strategies.

When you decode IMbs correctly, ordinary postage becomes a data‑rich marketing channel that drives smarter decisions and higher ROI.

Ensure Accurate IMB Readings With the Experts at Presort

Reading an Intelligent Mail Barcode is more than a technical exercise—it’s the gateway to faster delivery, superior tracking, and full USPS compliance. Presort’s mailing services generate, print, and verify millions of IMBs every month, giving clients confidence that each piece will sail through postal automation and deliver actionable data. From list hygiene and ZIP+4 appends to Full‑Service certification, we handle the details so you can focus on strategy.

Ready to unlock the full potential of Intelligent Mail®? Partner with Presort and put every barcode to work for your business.