Direct Mail

Intelligent Mail Barcode (IMB)

By 27 February 2024April 15th, 2024No Comments
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Intelligent Mail Barcode

Most direct mail marketers send hundreds and thousands of mail items every week or month. They are constantly looking for exploring new and better options to reduce marketing costs and conduct campaigns that can drive excellent results. The USPS offers several types of postal discounts to direct mail marketers. Dropshipping, bulk mailing, presorting, and commingling are some examples through which marketers can avail of huge discounts.

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The USPS moves millions of mail pieces per day and has built a well-spread logistics infrastructure to go about their operations smoothly. The Intelligent Mail Barcode (IMB) system is one of the most prominent aspects of this infrastructure, which we will discuss in more detail further.

What Is an Intelligent Mail Barcode (IMB)?

IMBs are 65-bar postal service barcodes that are assigned to every mailpiece. These barcodes include a lot of details about the mailpiece that helps the USPS sort and deliver it easily.

Initially, the IMB system was developed by the USPS for internal use only. Some high-speed automated sorting equipment can read the IMBs and route mail items to their respective destinations as per the encoded data.

Marketers that use these barcodes for mailing receive automation discounts from the USPS. The IMB system is not only focused on smoothening mailing activities and saving costs but is a whole set of services that includes mail tracking. Therefore, marketers who wish to track their mail items can simply print IMBs on them and avail of these benefits. Please note that this system is only applicable for mailing within the US.

Earlier, the USPS used two barcode symbologies named POSTNET and PLANET. The POSTNET (Postal Numeric Encoding Technique) was used for directing mail. The barcodes contained half and full-heightened bars encoding ZIP or ZIP+4 codes. There could be a maximum of 14 digits in a POSTNET barcode.

Coming to PLANET (Postal Alpha Numeric Encoding Technique), this barcode was mainly used to identify and track items and had 12 or 14 digits. Both these barcode systems were used together as part of USPS’s CONFIRM service and were in operation until the IMB system superseded them. The IMB system includes the OneCodeCONFIRM service, also known as the Confirm service, along with OneCodeACS, commonly known as Address Change.

Previously, it was very difficult to ascertain the delivery date or even whether your mail was deliverable. Even if you manage to receive the status, it could take several days and weeks. But this scenario completely changed when the USPS introduced IMBs to track and sort mail items. Though it is optional to use IMBs, their several advantages and highly discounted rates make them a smart choice.

Mainly, there are two types of IMB tracing that mailers can avail of:
  • Destination IMB tracing provides mailers with mail processing information that can help them determine the delivery rates.
  • Origin IMB tracing is used to know what your customers do in response to your mail. It helps to know when and where your customers have mailed their replies.

Also Read: How to Send Certified Mail

Components of an IMB

What data does an IMB store? It is crucial to know about the bits of information an IMB contains so that it is possible to read an IMB or decode the data it contains. The 65 vertical bars of the IMB store 31 pieces of data related to the destination, mail option, discounts applicable, and more such details. The IMB barcodes help communicate these details to the sorting machines so that further operations can be carried out.

The Intelligent Mail Barcodes are made up of two sections – the tracking and routing code. The former section consists of information about the mailer and the unique mailpiece, wherein the latter consists of the destination ZIP code. The barcodes are made up of 20 to 31 digits of the data payload.

The first 20 digits of an IMB comprise the tracking code which is further divided into four parts and a routing code:

Barcode Identifier (BI)

The BI is an essential part of the IMB and always consists of two digits. It is assigned by the USPS and is used for encoding the presort identification, usually printed on the Optional Endorsement Line (OEL) in a human-readable format. The BI is also used for the USPS’s future use. Previously, OneCodeACS and OneCodeCONFIRM users were asked to enter ‘00’ as the 2-digit BI. The USPS would later fill in the required digits. Technically, the BI is always zero except when used for flat-size mail pieces eligible for automation prices that bear the Optional Endorsement Line. In this case, the BI should correspond to the printed OEL.

The second digit of the BI should be within the range of 0-4. 00–04, 10–14, 20–24, 30–34, 40–44, 50–54, 60–64, 70–74, 80–84, and 90–94 are the approvable encoding ranges that all mailers have to follow carefully.

Service Type Identifier (STID)

The STID is three digits and represents the mail class and any additional service or a combination of services that the mailer has requested. Defining a mail item as either Full Service or Basic (also referred to as Non-Automation) is one of these services. Moreover, the STIDs are used to state how the sender wants the USPS workers to treat “undeliverable as addressed” (UAA) mail. The STID can also determine the form of address verification and correction that the sender has requested if any.

Some examples of basic STIDs that can be used only for automation purposes are:

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

Mailer ID

A mailer identifier is either 6 or 9 digits and is assigned by the USPS to identify mailers (the company sending out the mail items). Oftentimes, the mailer ID is also called the customer ID. High-volume mailers receive 6-digit mailer IDs, whereas low-volume mailers are given 9-digit mailer IDs. In order to distinguish between the 6-digit and 9-digit mailer IDs, you should know that every 6-digit mailer ID begins with a digit within the range of 0-8, and every 9-digit ID starts with the digit 9.

The Mailer ID is required to appear on all US mail barcodes, except for Origin IMB tracing barcodes wherein the mailer ID fields are combined with the serial numbers. The mailer ID remains the same for all mail items sent by the same mailer.

Sequence Number

The sequence number also referred to as the serial number, is unique for every mail piece and can be used to identify specific recipients. It can be assigned either by the USPS or the mailer themselves. Mailers also have the option to use the same sequence number for the entire mailing rather than individual mail pieces. If a Full-Service discount is claimed, these numbers should be kept unique for at least 45 days from mailing.

Mailers must ensure that the sequence number is either 6 or 9 digits long, depending on the length of the mailer ID. If only six digits were used in the mailer ID, there should be nine digits in the sequence number and vice versa. The mailer ID and the sequence number should contain a total of 15 digits altogether. Every USPS Intelligent Mail Barcode must have a sequence number, except when the mailer has opted for Origin IMB tracing. The mailer can always add zeros to fill up fields if required and as per the USPS guidelines.

The routing code section of the post office IMB barcodes can be omitted and have zero digits. However, if it is added to the IMB, there is only one part to it called the Delivery Point ZIP code.

Delivery Point ZIP Code

It could contain either zero, five, nine, or eleven digits. Basically, the number of digits is decided by the different forms of writing ZIP codes. Many mailers stick with 5-digit ZIP codes, whereas some of them use ZIP+4 codes, which are always better to ensure deliverability. The additional two digits representing the delivery point are sometimes added to the ZIP codes. Hence, the length of this section can differ. The routing code was encoded the same way in the previously used POSTNET barcodes.

Let us have a tabulated look at all the IMB components:

Section Field Number of Digits Example
Tracking Code Barcode Identifier (BI) 2 (the second digit must always be within the 0-4 range) 72
Service Type Identifier (STID) 3 708
Mailer ID 6 or 9 978231742
Sequence Number 6 if 9 digits were used for the mailer ID, otherwise 9 536897
Routing Code Delivery Point ZIP Code 0, 5, 9, or 11 10461

The complete IMB digit string would look like 7270897823174253689710461

These numbers are then converted into barcodes using the IMB symbology.

The IMB Symbology

The encoded IMB barcodes use the 4-state barcode symbology. It is called the 4-state symbology because four distinct symbols are used. Moreover, IMBs are also referred to as the 4-State Customer Barcodes or 4CB due to this reason. The four kinds of symbols are the full bar, ascender, descender, and tracker, which helps build the 65 vertical bars of the US mail barcode. Every bar has a tracker. Ascenders and descenders are ‘half’ bars that ascend and descend from the tracker, respectively. A full bar is a combination of all of the other three symbols. Refer to the image below for a better understanding.

The letters T(tracker), F(full bar), A(ascender), and D(descender) are often used to represent the symbols for building the encoded string from the digit string we discussed in the above section.

Now, how to convert the digit string into an encoded string? The process is rather lengthy, which is why most mailers use a USPS Intelligent Mail Barcode generator or outsource the job to a print and mail solution provider like PostGrid.

Size and Placement

The size of an IMB should be within 22-24 bars per inch. The height and width of all IMBs must be in accordance with the USPS IMB specifications.

  • The bar width must be within 0.015” to 0.0025” (0.038 cm – 0.063 cm)
  • The space between two bars must be at least 0.012” (0.030 cm) and must never exceed 0.040” (0.101 cm)
  • The length of all full bars must be within the range of 0.125” to 0.165” (0.317 cm – 0.419 cm)
  • Trackers must be at least 0.039” high (0.100 cm) but should not exceed 0.057” (0.144 cm)

An Intelligent Mail Barcode generator can help you take care of these specifications.

IMBs can only be printed in designated areas of letters, flats, and postcards falling under the USPS size dimensions. It means that IMBs cannot be used for all types and sizes of mail. For being eligible to use IMBs on your letters, they should be at least 3.5” high and 5” wide. Letters cannot exceed 6.125” in length and 11.5” in breadth. The minimum dimensions are the same in the case of postcards, but postcards cannot cross 4.25” x 6”.

On letters, IMBs should be printed either on the barcode clear zone towards the lower right part of the envelope or the address block. For flats, the IMBs are supposed to be located on the address side of the mail item and at a minimum of 8.46 m away from the edges. Usually, they are printed just above the recipient's name and address.

The Intelligent Mail Barcode Decoder

How to read Intelligent Mail Barcodes?

It is not easy to either encode or decode the Intelligent Mail Barcodes. But, there are apps that can help you decode them.

There are three broad ways of using the IMB system:

  1. Full Service
  2. Basic Automation
  3. Non-Automation

Either way, it is crucial to decode your IMBs before actual use to test for accuracy.

The IMB system is completely based on computer algorithms

Once the encoded strings are converted into barcodes, the only way to decode and read them is by using an Intelligent Mail Barcode Decoder which could be available on a handheld device or computer.

The USPS offers an online encoder and decoder both at

For using this encoder/decoder, you have to enter the assigned letter for every symbol (F, T, A, D). The tool can encode and decode only according to these manual inputs, which is why you need to take care of accuracy.

How Does IMB Mail Items Move Through the USPS Mailstream?

Direct mail sent and managed through the IMB system goes through pretty complex processes and involves a lot of checkpoints. The mainstream can be broadly divided into four parts as below:

1. Printing and Mailing

Anyone can print and mail their items with Intelligent Mail Barcodes, but it is advisable to take the help of a commercial printing and mailing vendor for setting up IMB tracing or a direct mail automation API like PostGrid. The IMB coding is complicated, and it is better to work with someone who has the experience and the necessary equipment to print IMBs perfectly as per the USPS guidelines.

As discussed earlier, only mail items with the specified size, weight, and format can use IMBs. Mailers should also take into account the barcode and address locations before printing.

2. Deposit at the USPS Entry Facility

The first IMB scanning will take place at the USPS entry facility after a few hours of deposit. All IMB mail items must be sent to an “Entry Facility,” also known as the “Network Distribution Center” (NDC). NDCs are regional warehouses, and there are a total of 21 NDCs in the US. All outgoing mail is sent to an NDC for sorting and routing.

Every NDC has huge high-speed sorting equipment to route every mailpiece to the next checkpoint using Intelligent Mail Barcodes. The next checkpoint could be another NDC or a destination facility. Every mail piece is scanned several times during the NDC processing procedure.

3. Routing to the USPS Destination Facility

After the NDC, your mail items are sent to a USPS “Destination Facility” or “Sectional Center Facility.” These facilities route mailpieces between the NDCs and the post offices nearest to the destination. The mailpieces are scanned again at SCFs and are routed toward the local post offices. There are about 195 SCFs across the US, and each one of them covers one or more 3-digit ZIP code prefixes.

4. Sending Mail to Local Post Offices for Delivery

Once the post offices receive the IMB mail items, there are more scan events before the final delivery. The post office is where the final scan event is done. Sometimes, scan events are completed right when the mail is out for delivery through geofencing.

Benefits of Intelligent Mail Barcodes


Undoubtedly, the most popular benefit of using IMBs is the ability to track your mail items. Using IMBs, you can also verify your mail delivery. IMB tracking provides details such as the date, time, and location of the most recent scan event by the USPS. It also helps get an estimated delivery date for your mail items. However, the tracking details provided by the USPS are a bit difficult to read, and it can take a while to filter relevant details.

A new feature named “Informed Delivery” is introduced by the USPS under the IMB system. Before this feature came into operation, mailers weren’t able to track mail items in real time; only information regarding the last scan event was available. However, Informed Delivery informs mailers about the exact mail whereabouts, not outdated details from hours before. Moreover, with Informed Delivery, you can know whether your mail is deliverable a lot sooner.

Save Shipping Costs

Since the IMB system helps the USPS shorten delivery times, they save a lot on their sorting, routing, and overall production expenses. Hence, the savings are passed down to mailers in the form of presort and other postal discounts. Mailers can use IMBs to cut down mailing costs while also being able to track their mail. IMBs also enable Full-Service mailers to streamline all their permit processes. Now, they just need to have a single permit and account to send mail items to any domestic location. The Mail Anywhere service helps mailers save additional permit application fees.

Address Correction

The IMB system uses another USPS service called the OneCodeACS that maintains a list of all mail items that have been returned to the post office due to wrong, invalid, or undeliverable addresses. Mailers can simply check out this list online and update their mailing lists accordingly. This way, mailers can calculate delivery rates in advance. Hence, they can save on reshipping costs and wastage. This service can be used for first-class, standard, periodicals, and several more mail classes.

Multichannel Campaign

If you use direct mail as part of a large multichannel campaign, you would know how important it is to synchronize all the activities. When timing is so important, using IMBs to know your mail’s exact delivery date can be really helpful.

Use Insights to Improve Response Rates

Origin IMB tracing helps you know how your campaign is performing. IMBs are not just useful for tracking outgoing mail, but you can have a close look at which of your direct mail recipients are responding. Using this incoming mail data, marketers can tailor messages and conduct more impactful campaigns. Not to forget that an IMB makes your mail items look good with fewer barcodes.

How Can PostGrid Help You With Intelligent Mail Barcodes?

We have successfully established that Intelligent Mail Barcodes have several advantages and should be used by every mailer. But, it is important to note that encoding IMBs isn’t easy, and the coding behind them is complex. PostGrid can help you create and print IMBs accurately and also track your mail items in real-time effortlessly.

PostGrid can also enable mailers to access and use CASS-certified addresses that have been already processed by the NCOA service. Not only that, PostGrid’s print and mail API can assist you in everything related to your direct mail marketing activities. So, whether it is making good use of IMBs or overall conducting powerful direct mail campaigns, PostGrid has got you covered.

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