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A possible Intelligent Mail Barcode for the Wikimedia Foundation address
A possible Intelligent Mail Barcode for the Wikimedia Foundation address

The Intelligent Mail Barcode (IMb) is a 65-bar barcode for use on mail in the United States.[1] The term "Intelligent Mail" refers to services offered by the United States Postal Service for domestic mail delivery. The IM barcode is intended to provide greater information and functionality than its predecessors POSTNET and PLANET. An Intelligent Mail barcode has also been referred to as a One Code Solution and a 4-State Customer Barcode, abbreviated 4CB, 4-CB or USPS4CB. The complete specification can be found in USPS Document USPS-B-3200.[2] It effectively incorporates the routing ZIP code and tracking information included in previously used postal barcode standards.

The barcode is applied by the sender; the Postal Service required use of the Intelligent Mail barcode to qualify for automation prices beginning January 28, 2013.[3] Use of the barcode provides increased overall efficiency, including improved deliverability, and new services.


The four types of symbols in an Intelligent Mail barcode.
The four types of symbols in an Intelligent Mail barcode.

The Intelligent Mail barcode is a height-modulated barcode that encodes up to 31 decimal digits of mail-piece data into 65 vertical bars.[2]

The code is made up of four distinct symbols, which is why it was once referred to as the 4-State Customer Barcode. Each bar contains the central "tracker" portion, and may contain an ascender, descender, neither, or both (a "full bar").

The 65 bars represent 130 bits (or 39.13 decimal digits), grouped as ten 13-bit characters. Each character has 2, 5, 8, or 11 of its 13 bits set to one. The Hamming distance between characters is at least 2. Consequently, single-bit errors in a character can be detected (toggling one bit results in an invalid character). The characters are interleaved throughout the symbol.

The number of characters can be calculated from the binomial coefficient.

The total number of characters is two times 1365, or 2730. Log2(2730) is 11.41469 bits per group. So the 65 bars (or 130 bits) encode a 114-bit message.

The encoding includes an eleven-bit cyclic redundancy check (CRC) to detect, but not correct, errors. Subtracting the 11 CRC bits from the 114-bit message leaves an information payload of 103 bits (the specification sets one of those bits to zero). Consequently, 27 of the 130 bits are devoted to error detection.

Data payload

The IM barcode carries a data payload of 31 digits representing the following elements:

Intelligent Mail barcode components
Index of first digit Length Name
1 2 Barcode identifier
3 3 Service type identifier
6 6 or 9 Mailer ID
12 or 15 9 or 6 Sequence number
21 11 Delivery point ZIP code

Barcode identifier

A Barcode Identifier is assigned by the United States Postal Service to encode the presort identification that is currently printed in human readable form on the optional endorsement line (OEL). It is also available for future United States Postal Service use. This is accomplished using two digits, with the second digit in the range of 0–4. The allowable encoding ranges are 00–04, 10–14, 20–24, 30–34, 40–44, 50–54, 60–64, 70–74, 80–84, and 90–94.

The first digit of the Barcode Identifier is defined as:

Value OEL Description
0x Default / No OEL Information
1x Carrier Route (CR), Enhanced Carrier Route (ECR), and FIRM
2x 5-Digit/Scheme
3x 3-Digit/Scheme
4x Area Distribution Center (ADC)
5x Mixed Area Distribution Center (MADC), Origin Mixed ADC (OMX)

Service type identifier (STID)

A three-digit value represents both the class of the mail (such as first-class, standard mail, or periodical), and any services requested by the sender.

Basic STIDs, for the purpose of automation only, are as follows:

Value STID Description
300 First-Class Mail with no services
261 Standard Mail with no services
040 First Class Mail, Basic option with Destination IMb Tracing[4]
042 Standard Mail, Basic option with Destination IMb Tracing[4]
044 Periodicals with manual address correction
401 Bound Printed Matter with no services
708 Business Reply Mail with no services
710 Priority Mail with no services
712 Priority Mail Flat Rate with no services

For a detailed list of STIDs, see Appendix A of the USPS Guide to Intelligent Mail Letters and Flats[5] or Service Type Identifiers.[6]

Mailer ID

A six- or nine-digit number assigned by the United States Postal Service identifies the specific business sending the mailing. Higher volume mailers are eligible to receive six-digit Mailer IDs, which have a larger range of associated sequence numbers; lower volume mailers receive nine-digit Mailer IDs. To make it possible to distinguish six-digit IDs from nine-digit IDs, all six-digit IDs begin with a digit between 0 and 8, inclusive, while all nine-digit IDs begin with the digit 9.

Sequence Number

A mailer-assigned six- or nine-digit ID specific to one piece of mail, to identify the specific recipient or household. The mailer must ensure that this number remains unique for a 45-day period after the mail is sent if a Full Service discount is claimed; otherwise, it does not have to be unique. The Sequence Number is either six or nine digits, based on the length of the Mailer ID. If the Mailer ID is six digits long, then the Sequence Number is nine digits long, and vice versa, so that there will always be fifteen digits in total when the Mailer ID and the Sequence Number are combined.

Delivery point ZIP code

This section of the code may be omitted, but if it is present, the five-, nine-, or eleven-digit forms of the ZIP code are also encoded in the Intelligent Mail barcode. The full eleven-digit form includes the standard five-digit ZIP code, the ZIP + 4 code, and a two-digit code indicating the exact delivery point. This is the same information that was encoded in the POSTNET barcode, which the Intelligent Mail barcode replaces.


Barcodes can be printed directly on documents to display through a window envelope or onto envelopes at various points in the mailing process. Many large companies use some or all of these approaches based on business needs, environment, as well as the unique characteristics of an application.[7]

Document composition

Over the years, more and more companies have been applying barcodes as part of document creation, with all barcode information included in the initial data payload. This trend has been driven by other initiatives, such as transpromotional transaction documents, where the goal is to produce individualized, relevant statements. Creating barcodes at this point in the process may require some added effort, but with the proximity to databases and business applications, some mailers may find it easier to track data back to its original data source (for example, to correct an address).

Document production

With today's document output technologies, mailers can modify and reengineer print streams, moving and adding information (such as barcodes) on the fly. Likewise, mailers can print barcodes directly on envelopes using an envelope finishing system. Either way, this approach enables mailers to centralize and standardize barcode creation on the production floor using the original data files without impacting upstream business applications.

Post-composition document re-engineering

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Many organizations may not be able to place Intelligent Mail Barcodes during the document composition step. There may not be sufficient resources to make the production modifications, or the transaction print data stream may arrive already composed, without the capability to reach back and change the composition process. But the organization may still want to place the code into the electronic document before it is printed, rather than later in a post-print production process.

Adding Intelligent Mail barcodes post-composition into the electronic print file allows organizations to simultaneously clean up all their transaction print streams while adding the codes they need. Other document re-engineering options can also be made at this step, such as adding 2D barcodes for use by the newer Automated Document Factory systems, checking address blocks, and adding more marketing messages.

Electronic commingling

Many organizations find that by commingling multiple smaller print streams before printing into one larger stream (or a few larger streams, sorted by criteria such as weight or number of inserts) they can gain efficiencies and reduce overall postage costs. During this electronic commingling process IMBs can be added to the documents and mail pieces in the new stream(s). This is an option to in-house sortation.

In-house sorting

When mailers run separate jobs and then want to combine them to achieve additional postal savings, they can physically sort mail after it is produced using sorter equipment. With new or upgraded sorter technology, mailers can accommodate the new Intelligent Mail barcode at the end of the mail production process. This is an option to electronic commingling.

Third-party presorting

Third-party presort houses provide mailers an easy way to comply with Intelligent Mail mandates and also provide them with the benefits of commingled mail. Even if a third-party applies the barcode, however, it may still be possible for the United States Postal Service to monitor the quality of the sortation using a mailer's unique Mailer ID. It is important for mailers to coordinate sequence numbers with their vendor so they can leverage OneCode ACS and OneCode Confirm services.


  1. ^ "steps-to-creating-intelligent-mail-barcode.pdf" (PDF). United States Postal Service Retrieved 2021-08-20.((cite web)): CS1 maint: url-status (link)
  2. ^ a b "Intelligent Mail Barcode 4-State Specification (Rev H)" (PDF). United States Postal Service. April 20, 2015. p. 1. Retrieved 2019-10-10.
  3. ^ "Intelligent Mail Services Latest News" (PDF). United States Postal Service. September 21, 2012. Retrieved 2012-09-27. The Intelligent Mail barcode, formerly referred to as the 4-State Customer barcode, is a new Postal Service barcode used to sort and track letters and flats. The Postal Service is promoting use of the Intelligent Mail barcode because it expands the ability to track individual mailpieces and provides customers with greater visibility into the mailstream.
  4. ^ a b IMb Tracing User Guide (PDF). USPS. January 9, 2012. p. 13.
  5. ^ USPS Guide to Intelligent Mail Letters and Flats
  6. ^ Service Type Identifiers, retrieved 2020-09-22
  7. ^ "Implementing the Intelligent Mail Barcode" (PDF). Pitney Bowes. 2008-09-23. Retrieved 2010-12-19. Based on the final USPS Federal Register Notice, mailers looking to take advantage of the lowest automation prices will need to replace the current POSTNET barcode with the new Full-Service Intelligent Mail barcode in the fall of 2009. .... The USPS will provide mailers with two options: Full-Service and Basic. The Basic option will have fewer requirements. The Full-Service option will provide access to more services (such as free ACSTM and Start the Clock information*) and will enable mailers to earn the greatest postal discounts as of the fall of 2009.