Skip links

An Ultimate Guide to Intelligent Mail Barcode (IMb)

Discover the ease of tracking, cost-effectiveness, and enhanced precision that IMbs bring to your direct mail strategies—all within your budget.

IMb is a barcode service offered by the United States Postal Service (USPS), streamlining direct mail tracking and sorting through a single barcode system. It encodes vital information for each mail piece, including date, time, location, and sorting operations, facilitating efficient and accurate mail processing. Direct mail marketers can leverage this data to optimize campaign efficiency and boost sales.

Furthermore, the USPS offers several postal discounts to direct mail marketers, including dropshipping, bulk mailing, and presorting.

How does an Intelligent Mail Barcode (IMb) Work?

The IMb system is integral to USPS’s logistics infrastructure, allowing them to sort and deliver millions of pieces of mail daily. An Intelligent Mail Barcode (IMb) is a 65-bar postal service barcode assigned to every mail piece. IMbs are encoded with information about the mail piece, such as the sender’s and recipient’s addresses, distribution center, carrier route, mail type, and the date and time of mailing that can be read automatically by the USPS mail sorting machines.

High-speed automated sorting equipment can read the encoded data on IMbs to route the mail items to the destination accurately. When direct mail marketers use these barcodes for mailing, they receive automation discounts from the USPS. This system is only applicable for mailing within the US.

In the past, finding out the delivery date or confirming mail delivery was time-consuming. Even if you somehow tracked the status, the delivery could take days or even weeks to occur. The whole scenario changed when the USPS introduced the IMb system for tracking and sorting mail items. While opting for this service in your mailing process is optional, its advantages and discounted rates make it a smart choice for you.

What are the Components of an IMb?

The 65 vertical bars of the IMb contain 31 pieces of data related to the destination, mail option, applicable discounts, and more. The IMb barcodes are made up of two sections – the tracking code and the routing code. The tracking code has details about the mailer and the unique mailpiece. In contrast, the routing code contains the destination ZIP code information. These barcodes comprise 20 to 31 digits of the data payload.

The tracking code is further divided into five parts:

  1. Barcode Identifier (BI)

BI is a two-digit number that is assigned to each IMb. It is assigned by the USPS and is used to encode the presort identification, usually printed on the Optional Endorsement Line (OEL) in a human-readable form. 

Previously, the users of OneCodeACS and OneCodeCONFIRM were asked to enter “00” as BI. The USPS would then fill in the required digits. Technically, BI is always zero except when used for flat-size mail pieces eligible for automation prices that bear the OEL. Here, the BI must correspond to the printed OEL.

The second digit of the BI must be between the range of 0-4. The following encoding ranges are approvable for all mailers: 00–04, 10–14, 20–24, 30–34, 40–44, 50–54, 60–64, 70–74, 80–84, and 90–94.

  1. Service Type Identifier (STID)

The Service Type Identifier (STID) is a three-digit code that helps USPS identify the class of mail and any additional services you have requested so they can deliver your mail quickly and accurately. Defining a mail item as either Full Service or Basic comes under these services. Likewise, the STIDs are used to state how the sender wants the USPS to treat ‘undeliverable as addressed’ (UAA) mail.  

Below are some examples of basic STIDs that can be used only for automation:

  • 040 – First class mail, basic with destination IMb tracing
  • 042 – Standard mail, basic with destination IMb tracing
  • 044 – Periodicals, manual address correction
  • 261 – Standard mail, no services
  • 300 – First class mail, no services
  • 401 – Bound printed matter, no services
  • 708 – Business reply mail, no services
  • 710 – Priority mail, no services
  • 712 – Priority mail flat rate, no services
  1. Mailer ID

Mailer identifiers are the unique numbers USPS assigns to businesses and organizations that send mail. They are used to identify the sender of a mail piece and track its delivery and are also called customer IDs.

 These mail identifiers can either be 6 or 9 digits long. 6-digit mailer IDs are assigned to high-volume mailers, whereas 9-digit mailer IDs are assigned to low-volume mailers. All the 6-digit mailer IDs start with a number between 0 and 8, while the 9-digit mailer IDs begin with the number 9.

  1. Sequence Number

The sequence number is a unique number for each mail piece that can be used to identify individual recipients. It can be assigned either by USPS or the mailer. Mailers can choose to use the same sequence number for all mail pieces in a mail. But if the mailer claims a full-service discount, the sequence numbers must be unique for at least 45 days after mailing. 

The sequence number of the mail must be six or nine digits long, depending on the length of the mailer ID. If the mailer ID is 6 digits long, the sequence number must be 9 digits long, and vice-versa. The total number of digits must be 15.

Every USPS IMb must have a sequence number unless the mailer uses Origin IMb tracing. Mailers also have the option to add zeros to fill up the sequence number if required.

The routing code section of the USPS IMb can be omitted or have up to 11 digits. If it is included in the IMb, it only contains the ‘Delivery Point ZIP Code.’

  1. Delivery Point ZIP Code

A ZIP code can have 0, 5, 9, or 11 digits. The number of digits depends on how it is written. Most people use 5-digit ZIP codes, but some use ZIP+4 codes, which are always better to ensure deliverability. The extra 2 digits show the delivery point and can change the length of the ZIP code. In the past, the routing code was encoded in the same way as the POSTNET barcodes. 

SectionFieldNumber of DigitsExample
Tracking CodeBarcode Identifier (BI)2 (the second digit must always be within the 0-4 range)72
Service Type Identifier3708
Mailer ID6 or 9978231742
Sequence Number6 if 9 digits were used for the mailer ID, otherwise 9536897
Routing CodeDelivery Point ZIP Code0, 5, 9, or 1110461


The complete IMb digit string would look like 7270897823174253689710461

The IMb symbology is used to turn the number into barcodes.

Symbols Used in IMb

IMb uses a four-state barcode symbology. It means four different symbols are used to encode data. Due to this reason, IMbs are also referred to as the 4-State Customer Barcodes or 4CB. 

The four kinds of symbols are:

  1. Full bar
  2. Ascender
  3. Descender
  4. Tracker

Each symbol is made of a different combination of vertical bars. IMbs have 65 vertical bars, and each bar has a tracker. Ascenders and descenders are half-bars extending above or below the tracker. A full bar is a combination of all three symbols.

The IMb uses four symbols to build the encoded string, often represented by the letters T (tracker), F (full bar), A (ascender), and D (descender).

Converting a digit string into an encoded string is a complex process. Due to this, most mailers use the USPS IMb generator or outsource the job to a print and mail solution provider like Compu-Mail due to increased efficiency and accuracy.

IMb Size & Placement

IMbs must be printed to certain specifications to ensure the USPS can accurately scan and process them.

  1. The size of an IMb should be between 22 and 24 bars per inch.
  2. The bar width should be between 0.015” to 0.0025” (0.038 cm – 0.063 cm).
  3. The space between two bars should be at least 0.012” (0.030 cm) and no more than 0.040” (0.101 cm).
  4. The length of all full bars must be between 0.125” (0.317 cm) and 0.165” (0.419 cm).
  5. Trackers must be at least 0.039” (0.100 cm) high but no more than 0.057” (0.144 cm).

An IMb generator can help you create IMbs that fulfill all these specifications.

IMbs can only be printed on certain areas of letters, flats, and postcards that meet the USPS size requirements. It means not all mail types and sizes can utilize IMbs. To use IMbs on letters, it should be at least 3.5 inches in height and 5 inches in width, and the maximum length can go up to 6.125 inches and width up to 11.5 inches. The minimum dimensions in the case of postcards remain the same, but the maximum limit cannot be more than 4.25” x 6”.

On letters, IMbs can be printed in two places: the barcode clear zone towards the lower right part of the envelope or the address block. On flats, IMbs must be printed on the address side of the mail item, at least ⅛ inch away from the edges. They are usually printed just above the recipient’s name and address.

Advantages of the Intelligent Mail Barcode

The Intelligent Mail Barcode offers several advantages to both mailers and the USPS, including:

  1. Tracking

The biggest benefit of using IMbs is the ability to track mail items. It is also used to verify deliveries. IMb tracking provides details such as the date, time, and location of the most recent USPS scan event and an estimated delivery date. 

USPS has introduced a new feature called Informed Delivery® under the IMb system. Before introducing this feature, businesses could not track mail in real-time. However, Informed Delivery® provides mailers with the exact location of the mail.  

  1. Save Shipping Costs

The IMb system helps the USPS save money on sorting, routing, and production costs. Due to this, the USPS processes mail more efficiently and accurately. Further, the USPS passes these savings on to mailers through presort and other postal discounts. 

IMbs also makes it easier for Full-Service mailers to manage their permits. With IMbs, Full-Service mailers only need a single permit and account to mail items to any domestic location. Another service named Mail Anywhere can help mailers save even more on permit application fees.

  1. Address Correction

The IMb system uses the OneCodeACS service to track undeliverable mail. Mailers can access the tracking information online to update their mailing lists and calculate delivery rates. It helps mailers save money on reshipping costs. OneCodeACS can be used for first-class, standard, periodicals, and several more mail classes.

  1. Multichannel Campaign

If you use direct mail as part of a large multichannel marketing campaign, it is important to synchronize all of your marketing activities. IMbs can be used to track the exact delivery date of your mail. 

IMbs can also help ensure that your direct mail arrives at the same time as your other marketing messages, such as email and social media posts. It can help increase the effectiveness of your overall campaign.

  1. Use Insights to Improve Response Rates

Origin IMb tracing helps track the performance of direct mail campaigns. You can check which recipients respond to your mailers and use this data for future campaigns. IMbs can also make your mail look more professional using fewer barcodes.

How Do IMb Mail Items Move Through the USPS Mailstream?

Sending and handling direct mail using the IMb system involves many steps and checks. The main process can be broadly divided into four parts:

  1. Printing and Mailing

Anyone can print and mail their mail pieces with IMbs. However, working with a commercial printing and mailing vendor or a direct mail automation platform like Compu-Mail can make your tasks much easier. IMb coding is complex, and working with someone with the experience and equipment to print IMbs according to USPS guidelines is important.

Do note that only the mail pieces with specified size, weight, and format can use IMbs. Mailers should also ensure to print the IMb in the designated area on the mail item.

  1. Depositing at the USPS Entry Facility

The first time your IMb mail will be scanned is at the USPS entry facility a few hours after depositing your bulk mail. This entry facility is also known as Network Distribution Center (NDC). NDCs are regional warehouses where all the outgoing mail is sorted and routed.

Every NDC has large, high-speed sorting machines that use IMbs to route each mail piece to its next destination. It could either be another NDC or the final delivery facility. Every mail piece is scanned multiple times during the NDC processing procedure. 

  1. Routing to the USPS Destination Facility

After the NDC, your mail is sent to a USPS Destination Facility or Sectional Center Facility (SCF). The facilities are responsible for sorting and routing mail between the NDC and local post offices nearest to the destination. The mail is again scanned at SCFs and routed to the local post offices. There are around 195 SCFs across the US, each covering one or more 3-digit ZIP code prefixes.

  1. Sending Mail to Local Post Offices for Delivery

After IMB mail pieces are received at the post office, they may be scanned several times before final delivery. The last scan typically takes place at the post office, but sometimes, scan events can happen even after the mail is out for delivery through a process called geofencing.

How Can Compu-Mail Help You With Intelligent Mail Barcodes?

Creating and printing accurate IMBs is a process that requires careful attention to detail..With a dedicated and experienced team, we at Compu-Mail ensure the proper utilization and placement of IMBs on mail pieces. Moreover, our team maintains up-to-date USPS Mail Design Professional Certifications. This ensures that businesses investing in our services receive optimal results and effectiveness in their direct mail campaigns.

Furthermore, Compu-Mail allows you to seamlessly and accurately create & print IMbs. It helps streamline your printing and mailing processes and track your mail pieces in real-time. Compu-Mail’s print and mail platform can also help you with all aspects of your direct mail marketing efforts. Whether optimizing IMbs or running effective direct mail campaigns, Compu-Mail fully supports it.

Contact us for any questions or assistance on direct mail campaigns.

Frequently Asked Questions

Q: How is IMb read?

A: The IMb is broken into two parts — the tracking code and the routing code. The tracking code gives information about the mailer’s identification plus unique mailpiece information, and the routing code defines the Delivery Point Zip code.

Q: What information can I get from IMb tracking data?

A: IMb tracking can provide you with relevant information about your direct mail campaigns, including:

  1. Delivery status
  2. Scan events
  3. Delayed deliveries
  4. Undeliverable mail pieces

Q: What are the Types of IMb Tracing?

There are two types of IMb tracing that you can avail of:

  1. Destination IMb Tracing

It provides the mail processing information to help you determine the delivery rates.

  1. Origin IMb Tracing

It is used to determine how customers respond to your mail. It helps you determine when and where your customers have mailed their replies.