What are Intelligent Mail Barcodes?

What is an Intelligent Mail Barcode

Share This Post

In the Internet era it’s easy to forget about the enduring importance of postal services. However, many businesses and organisations still rely heavily on physical mail to communicate and deliver important documents, products, and more.

The United States Postal Service (USPS) reports that a whopping 127.3 billion pieces of mail were sent in 2022 across the United States. It’s clear that despite advancements in technology, postal services remain crucial for facilitating communication.

Therefore, to keep the postal services efficient and accurate, the U.S. Postal Service (USPS) introduced the Intelligent Mail barcode (or IMb for short) in 2009. IMb is an updated version of the existing Postnet Barcode system, first developed in the 1990s.

In this article, we will explore the Intelligent Mail barcode, discussing its types, how it operates, and its structure. We will also provide guidelines regarding design and printing standards for the IMb barcodes. By reading this article, you will gain an in-depth understanding of the IMb and how to use it effectively.

So without further ado, let’s get started.

What is an Intelligent Mail Barcode?

Intelligent Mail Barcode

The Intelligent Mail barcode is a 65-bar barcode symbology used by the USPS to identify and track mail pieces as they move through the postal system. It combines routing and tracking information into a single barcode, allowing postal services to manage their workloads better and streamline the delivery process.

Intelligent Mail barcodes are also known as One Code Solutions and 4-State Customer Barcodes, abbreviated 4CB, 4-CB, or USPS4CB. They are a type of linear barcode symbology, meaning the information is encoded in a series of vertical stripes or “bars” and spaces.

Intelligent Mail barcodes can only encode numerical digits ranging from 0 to 9. These barcodes can hold between 20 to 31 characters worth of information about a piece of mail. 

Before the implementation of IMBs by the USPS, it was a strenuous task to track your mail delivery, and oftentimes there would be no updates at all. There would be a delay of days, sometimes even weeks, without any information on the delivery status. However, the introduction of IMBs completely revolutionized this situation, making mail tracking and sorting easy and efficient.

The Intelligent Mail barcode system replaced the existing Postnet barcodes and PLANET barcodes, which were used for the same purpose. Check out our articles on what is Postnet barcode and what is PLANET barcode to learn about these barcode symbols.

Intelligent Mail barcodes were first introduced in 2009 and used for internal operations. However, beginning January 28, 2013, the IMb barcode became mandatory for all commercial mailers and direct mail marketers who wanted to qualify for automation discounts from USPS.

How to Recognise Intelligent Mail Barcodes?

An Intelligent Mail barcode can easily be recognised due to its unique appearance. The barcode has a fixed length of 65 bars. These bars are height-modulated, meaning the length of vertical bars and vary in order to express the encoded data.

The IMb also has four-state encoders (also known as bar states) called Full Bar, Ascender, Descender, and Tracker. These four-state encoders represent four different patterns of short and long bars, making it easier to identify the barcode.

How to Recognise Intelligent Mail Barcodes

Why Do We Need an Intelligent Mail Barcode?

Intelligent Mail barcodes allow USPS to identify a piece of mail quickly and provide the necessary data to make their sorting process more efficient and accurate.

Intelligent Mail barcodes allow mailers to participate in multiple Postal Service programs simultaneously by using the same barcode. This simplifies the mailing process and saves costs.

Intelligent Mail barcodes also provide improved mail flow monitoring as it allows tracking mail items during each delivery process. This provides the mailer and the receiver greater visibility and control of their mail.

Using IMb is necessary for automating mail services such as First-Class Mail postcards, Insured Mail and Certified Mail.

Variants of the Intelligent Mail Barcode

The USPS has developed different Intelligent Mail barcodes to cater to different needs. These are.

  • Intelligent Mail package barcodes
  • Intelligent Mail tray label
  • Intelligent Mail container barcodes

Intelligent Mail Package Barcodes (IMpB)

Intelligent Mail package barcodes are a type of barcode that can be read by automated parcel processing equipment and scanning devices. These barcodes are used where automatic package tracking is required.

The Intelligent Mail package Barcode uses the GS1-128 barcode symbology instead of the IMB symbology.

Intelligent Mail Tray Label

Intelligent Mail Tray label is used in the logistics industry to sort mail items into trays, tubs, and sacks. It has a 24-digit Intelligent Mail Tray barcode that is encoded using the GS1 Code 128 symbology.

Intelligent Mail Container Barcodes (IMCb)

The Intelligent Mail Container Barcode (IMCB) enables mailers to generate container labels with barcodes that can be scanned at various transportation and processing points. IMCb helps track mail container movement throughout the entire delivery process.

How Do IMb Mail Items Move Through the USPS Mailstream?

Six steps on how does a mail move in USPS Mailstream

The process of sending and managing direct mail through the IMB system includes several complex steps and checkpoints. It can be divided into four main parts.

  1. Printing and mailing
  2. Deposit at USPS entry facility
  3. Routing to USPS destination facility
  4. Arrival at local post offices for delivery

Printing and Mailing

The first step of the process is to print and attach the IMB barcodes. This step requires a valid IMb barcode that can be printed on the mail item.

Although it is possible for anyone to print and mail items using Intelligent Mail Barcodes, it is recommended to seek assistance from a commercial printing and mailing vendor for setting up IMB tracing or a direct mail automation API. This is because the IMB coding is complicated, and it is better to work with someone who has the experience and the necessary equipment to print IMBs as per the USPS guidelines.

Deposit at the USPS Entry Facility

Once the mail items are printed and ready to be sent, they must be deposited at the nearest USPS Entry Facility (also referred to as the “Network Distribution Center” (NDC)). There are 21 NDCs (regional warehouses) in the US. All outgoing mail is sorted and routed by these NDCs.

Each NDC is equipped with large high-speed sorting machinery and intelligent mail barcode decoders that uses Intelligent Mail barcodes to sort each mail item and direct them to the next checkpoint. The checkpoint could either be another NDC or a destination facility. The mail pieces are scanned multiple times throughout the entire NDC processing process.

Routing to the USPS Destination Facility

Once your mail items have gone through the NDC, they will be sent to a USPS facility called the “Destination Facility” or “Sectional Center Facility”. These facilities will then direct your mail pieces to the post offices closest to their final destination. The mail items will be scanned once again at the SCFs before being sent to the local post offices. 

The US has approximately 195 SCFs, each including one or more 3-digit ZIP code prefixes.

Sending Mail to Local Post Offices for Delivery

The last step of the process is to send the mail items to their respective local post office. They will be sorted and sent to a carrier route for delivery to the final destination. Post offices also conduct additional scans, with the final being at delivery time.

Structure of Intelligent Mail Barcodes

Detailed structure of Intelligent Mail Barcode

An Intelligent Mail barcode consists of the following elements.

  • Leading quiet zone
  • Tracking code component (20 digits) that consists of the following fields. 
  • Barcode identifier
  • Service type identifier
  • Mailer ID
  • Origin IMb tracing customer number
  • Mail processing equipment type
  • Mail processing equipment number
  • Date
  • Time
  • Serial number or sequence number
  • Routing code component that consists of the delivery point ZIP Code (0, 5, 9, or 11 digits)
  • Trailing quiet zone

The IMB code is a four-state symbology that uses four different bars to represent each symbol character. The four state names are listed below.

  • T (tracker)
  • D (descender)
  • A (ascender)
  • F (full bar)

Components of Intelligent Mail Barcodes

Components of Intelligent Mail Barcodes

IMb has 65 vertical bars that store up to 31 characters, including details about the recipient, mail preferences, applicable discounts, and other relevant information. IMB barcodes can easily communicate this information to sorting machines, allowing for efficient and accurate mail processing.

IMb has two parts: the Tracking code and the Routing code. Here is a table providing a quick overview of Intelligent Mail Barcode Components.

Number of Digits
Tracking Code
Barcode Identifier
Service Type Identifier
Mailer ID
6 or 9
Sequence Number
6 – if Mailer ID is 9 digits; 9 – if Mailer ID is 6 digits
Routing Code
Delivery Point ZIP Code
0, 5, 9 or 11

The IMB Tracking Code

The IMB Tracking code includes information about the sender and mailpiece and can be broken down into the following components.

  • Barcode Identifier (BI) (2 digits)
  • Service Type Identifier (STID) (3 digits)
  • Mailer ID (6 or 9 digits)
  • Sequence Number (6 or 9 digits)

Barcode Identifier (BI)

Barcode Identifier (BI) is the first two digits of the Intelligent Mail barcode and is assigned by the USPS. It encodes presort identification information printed on the Optional Endorsement Line (OEL) in a human-readable format.

Previously, OneCodeACS and OneCodeCONFIRM users were instructed to enter ’00’ as the 2-digit Barcode Identifier, with USPS filling in the remaining digits. Specifically, the BI is always zero, except for certain flat-size mail pieces with an OEL. If a flat-size mail piece has an OEL, the BI must correspond with the printed OEL.

The Barcode Identifier is mandatory for all IMB users and should not be left blank or changed without the approval of the Postal Service.

Service Type Identifier (STID)

The Service Type Identifier (STID) is a three-digit code used to identify the mail class (such as first-class, standard mail, or periodical) and the type of service or combination of services requested by a mailer. It can also be used to indicate how the sender wants UAA (undeliverable as addressed) items treated and what form of address verification and correction they have requested, if any.

Full Service or Basic (also called Non-Automation) are two of the most common services associated with STIDs, allowing senders to determine how their mail will be processed.

Full-Service provides access to services such as tracking, electronic documentation, delivery confirmation, return receipt and other features. On the other hand, Basic service is used when a mailer does not take advantage of any additional service beyond first-class postage payment.

Here are some examples of basic STIDs that can only be used for automation.

STID Description
First class mail, basic option with destination IMB tracing
Standard mail, basic option with destination IMB tracing
Periodicals with manual address correction
Standard mail with no services
First class mail with no services
Bound printed matter with no services
Business reply mail with no services
Priority mail with no services
Priority mail flat rate with no services

See Appendix A: Appendix A: Ancillary Service Type Identifier (STID) Details of USPS Guide for a complete list of STIDs

Mailer ID

The Mailer ID (also called Mailer Identifier or MID) is a unique six or nine-digit number assigned by the USPS that identifies the mailer. It ensures accurate tracing and monitoring of outgoing mail and is also called the Customer ID. The Mailer ID remains the same for all mail items sent by the same mailer.

All six-digit Mailer IDs start with a digit between 0 and 8 and are assigned to higher-volume mailers as it has a larger sequence number range. On the other hand, all nine-digit Mailer IDs start with the digit 9 and are assigned to low-volume mailers.

The Mailer ID is necessary for all IMB codes except those using Origin IMB Tracing barcodes. In the case of Origin IMB Tracing barcodes, the Mailer ID is merged with the Sequence Number field. 

Sequence Number

The Sequence Number, also called Serial Number, are six or nine-digit code used to identify the specific recipient or household. The Sequence Number can be assigned by either the mailer or the USPS.

The length of the Sequence Number depends on the Mailer ID. When the Mailer ID has six digits, the Sequence Number will have nine digits, and vice versa. The combined total of the two fields should always be fifteen digits. If the two fields do not add up to fifteen digits, leading zeros should be used to fill out the field completely.

For Intelligent Mail Barcodes, having a Sequence Number is mandatory unless the mailers opt for Origin IMB tracing. To fill in fields when required, according to USPS guidelines, zero padding must be done by mailers.

IMB Routing Code

The IMB Routing code consists of information about the carrier route and delivery. The number of digits in the routing code depends on how much information the mailer includes. It can be either zero, five, nine, or eleven digits long.

The Routing code has a single component known as the Delivery Point ZIP code.

Delivery Point ZIP Code

The ZIP code (Zone Improvement Plan) is a system used by the USPS to identify the geographic location of a receiver. The number of digits in the destination ZIP code can vary depending on the different writing formats. A zip code can have zero, five, nine, or eleven digits. 

How Do Mailers Benefit from the Intelligent Mail Barcodes?

The Intelligent Mail barcode offers the following benefits to mailers.

  • Stores more information than other existing postal barcodes.
  • Enables mailers to have additional digits to use for unique identification of up to one billion mailpieces per mailing.
  • Offers precise and comprehensive details about mailings that facilitate improved decision-making.
  • Enables users to take part in several USPS service programs using only one barcode symbology.

How to Get an Intelligent Mail Barcode?

To get an IMB code, follow these steps.

  • Download and install the encoder and the intelligent mail barcode font
  • Apply for a Mailer Identifier
  • Fill in the barcode fields
  • Combine everything together

Download and Install the Encoder and the Font

As previously mentioned, an Intelligent Mail barcode has a 20-digit tracking code and a Routing Code field of up to 11 digits. To convert these codes into a 65-character string and generate the bars that make up the IMb tracking code, users need an encoder. Additionally, a special font is needed to display the IMb tracking code.

Users can access the encoder and IMb tracking code fonts at USPS Intelligent Mail Barcode (IMb) Encoder Software and Fonts page.

Apply for a Mailer Identifier

To use IMb codes, mailers must possess a Mailer Identifier. New Mailer Identifiers are issued through the USPS Business Customer Gateway page via centralised Postal Service procedures. Based on established Postal Service standards, mail owners and preparers will receive a six- or nine-digit Mailer Identifier.

Fill in the Barcode Fields

To complete the barcode, mailers must fill out all five IMb fields, which include

  • Barcode Identifier
  • Service Type Identifier
  • Mailer ID
  • Serial Number
  • Routing Code

Depending on the length of the Mailer ID, the Serial Number will be either nine or six digits long. The Routing Code can include a 5-digit ZIP Code, a 9-digit ZIP+4® code, or an 11-digit delivery-point code.

Put Everything Together

After selecting service(s), receiving a Mailer ID, and strategizing a unique serial number, mailers can combine the five fields to create a 20-31 digit string. This string can be encoded to 65 characters and converted to a 65-bar Intelligent Mail Barcode using the IMb font.

The Intelligent Mail barcode can be placed in two locations on letters: the address block or the barcode clear zone. On flats, it should be at least 1/8 inch away from the edge on the address side.

How to Design Intelligent Mail Barcode? - Designing Best Practices

The United States Postal Service has created specific barcode design guidelines to ensure that the Intelligent Mail Barcode will be properly scanned and tracked throughout the mail stream. These guidelines cover several aspects, which are all critical to ensuring that the barcode can be read correctly by USPS scanners.

Let’s look at some best practices for designing an Intelligent Mail Barcode.

Design rule of barcode size of Intelligent Mail Barcode

Barcode Size

Barcode size refers to the overall size of the barcode. The USPS recommends that IMb codes should have a size of between 22-24 bars per inch.


The X-dimension is the width of the narrowest element in a barcode. With IMb, the X-dimension should be between 0.013 inches to 0.021 inches (0.33 mm – 0.53 mm).

Design rule for X-Dimension of Intelligent Mail Barcode
Point on design rule of barcode height of the Intelligent Mail Barcode

Barcode Height

Barcode height is the overall vertical size of the barcode. The USPS recommends that IMb codes should have a minimum height of 0.75 inches (19.05 mm).

Space Between Two Bars

Space between two bars is the amount of empty space between adjacent elements in a barcode. The minimum space required between the two bars of IMB is 0.012 inches (0.30 mm), while the maximum space shouldn’t exceed 0.040 inches (1.02 mm).

Design rules for space between two bars of Intelligent Mail Barcode
Design rule for length of full bars of Intelligent Mail Barcode

Length of Full Bars

Full bars (one of the four-state encoders) must have a length ranging between 0.125 inches – 0.165 inches (3.18 mm – 4.19 mm).

Height of Trackers

Trackers (one of the four-state encoders) should have a minimum height of 0.039 inches and a maximum of 0.057 inches (0.99 mm – 1.45 mm).

Two design rules for height of trackers of the Intelligent Mail Barcode
Five design rules for quiet zone of Intelligent Mail Barcode

Quiet Zone

A quiet zone is a white space around all four sides of a barcode.

The USPS recommends having quiet zones that are at least ten times the X-Dimension on all four sides of a code. USPS also mentions the minimum mandatory quiet zones, which are 0.25 inches (6.35 mm) at the start and end of the barcode and 0.125 inches (3.18 mm) above and below the barcode.

Barcode Density

The barcode density is the number of characters that can be encoded per inch. IMB barcode density should range between 20 to 24 bars per inch, with all bars evenly spaced.

Design rule of barcode density of Intelligent Mail Barcode

How to Print Intelligent Mail Barcode? - Printing Best Practises

In addition to design rules, using the right type of printer is important for accurate barcode scanning. For Intelligent Mail barcodes, it is recommended to use a high-quality thermal printer.

Thermal printers use heat to produce images on print media and are reliable, affordable, and fast. They don’t require ink or toner, making them ideal for large-scale printing. Refer to our guide on how thermal printer works for an explanation of the science behind their operation.

Triton Store provides a wide range of thermal printers from reputable brands like Honeywell, Zebra and TSC. Choose from direct thermal printers, thermal transfer printers, barcode label printers, desktop printers and industrial printers, all available at competitive prices.

If you’re looking for an efficient thermal printer, the Triton Store is the place to go!

How to Position Intelligent Mail Barcodes?

List of four points on positioning of Intelligent Mail Barcode

The USPS barcode scanners are designed to find and scan barcodes in a specific location on mail items. Therefore, mailers must correctly position Intelligent Mail barcodes in the designated area to ensure a successful scan.

Here are the USPS guidelines for positioning Intelligent Mail barcodes.

  • Should be placed on the lower right corner of the envelope or postcard and must be within the bounds of USPS size dimensions.
  • Should be placed 0.33 inches (8.46 mm) away from the edge of the mail item and preferably above the recipient’s address information.
  • Should not cross over any letter folds, perforations, or indentations
  • For letters, flats and postcards, the barcode must be 3.5 inches (88.90 mm) high and 5 inches (127 mm) wide from the edges.

Make Label Designing and Printing Easy With BarTender Software

Seagull Scientific’s BarTender software is the world’s most trusted label design and printing solution. BarTender allows you to quickly, accurately, and efficiently design, manage, automate, and print barcodes, labels, and tags.

BarTender software integrates seamlessly with existing business systems and infrastructure to facilitate label design and printing. The software supports connecting multiple data sources at once, including databases, CSV files, date/time, and serialisation, to create barcodes and labels effortlessly.

The software includes a vast library of 400 preformatted barcode components that are compliant with 105 barcode symbologies and over a dozen barcode standards. For more information, please consult our understanding BarTender software guide, which provides comprehensive details about this exceptional software.

Get unbeatable prices on all four editions of BarTender software at the Triton Store. Whether you need the Starter Edition, Professional Edition, Automation Edition and Enterprise Edition, or the latest cloud edition, BarTender Cloud, we’ve got you covered. Take advantage of our incredible offer and get your hands on BarTender today for the best value!

Want to learn more? Contact us via live chat or fill out a form here.

Frequently Asked Questions

Why Did the USPS Upgrade the Barcode System?

USPS upgraded the barcode system to make it easier and more efficient for tracking outgoing mail. The Intelligent Mail barcode contains data from both the old POSTNET and PLANET barcodes plus additional data fields, making it a more comprehensive system.

Intelligent Mail barcode is also capable of holding more information than previous versions but still takes up the same amount of space on the mailpiece.

What is IMb Tracing?

The IMb Tracing is a USPS service that enables mailers to track and obtain processing information about both outgoing and incoming reply mail. This processing information includes details such as date, time, location, and type of sorting performed at a Postal Service facility.


To sum it up, the Intelligent Mail barcode has integrated various functionalities that are vital to the modern-day postal service. With its precise tracking, verification of mail presence, and improved address quality, it has revolutionized the Postal Service.

In a world where everything is digital, Intelligent Mail barcode technology has provided reliability and security for mail delivery. It is a testament to the technological advancements the USPS has made over the years and USPS’s dedication to providing the best service they possibly can.

We hope this article was useful.

Thanks for reading!

Latest Articles

Learning Centres