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Intelligent Mail Package Barcode (IMpb)

The Intelligent Mail Package Barcode is the USPS-developed barcode on a package label that automated parcel equipment and scanners read. It holds the routing and tracking data USPS uses to sort and track each package. Shippers who meet its requirements get the best commercial prices and piece-level tracking at no extra charge for most products.

Updated October 31, 202625 sources

What it is

The IMpb is a data string encoded as a GS1-128 barcode, subset C. It joins the destination ZIP Code and the package identification code, the package's tracking number, in one barcode. Its length varies with the elements the mailer selects. USPS requires the IMpb or another unique tracking barcode on every parcel shipped through the Postal Service. IMpbs go on all commercial packages and on other pieces whose customers request extra services.

A channel code in each barcode matches the package to the payment channel that produced it. Commercial shippers print IMpbs, and so do online postage systems, PC Postage vendors and postage meters.

Shippers use the IMpb to get Commercial Base Pricing, which also requires an electronic file with the address data. They print it with IMpb-compliant software. USPS uses the barcode's routing data to sort packages on automated equipment. The barcode and its file let USPS plan workload before packages arrive.

The IMpb has a companion, the Intelligent Mail matrix barcode, a two-dimensional barcode that holds the same data. Two of them on a label give sorters two more chances to read a creased or distorted label.

How it works

Each package meets three requirements:

  1. It bears a unique IMpb.
  2. A Shipping Services File record of version 1.6 or higher goes with it.
  3. That record holds the correct delivery address or 11-digit Delivery Point Validated ZIP Code.

The Shipping Services File is the electronic file that holds all manifest and payment information. Each file holds at least one manifest.

A shipper sends the file in one of two ways. With eVS, one file carries manifest, tracking and postage, and postage comes out of a centralized account. With a Manifest Mailing Solution, the file carries manifest and tracking, and a separate postage statement pays. USPS has replaced eVS with USPS Ship.

Once the package enters the network, automated equipment reads the barcode to sort and track it to the delivering post office. USPS returns a scan event extract file with the package's tracking events. It also returns a confirmation/error/warning file that reports problems in the file's records.

An illustrative barcode for a commercial shipper with a nine-digit Mailer ID and a nine-digit ZIP Code.

4202210312349212391234567812345670

The Mailer ID and serial number are examples.

The barcode, field by field
FieldDigitsMeaning
Routing code420Always the same code; it marks the start of the destination ZIP Code.
Destination ZIP Code221031234Five or nine digits.
Channel92The payment channel; it is required to make the barcode unique.A commercial mailer with a nine-digit Mailer ID.
Service type code123Three digits naming the mail class, product and extra services.Priority Mail: Open and Distribute (PMOD)
Mailer ID912345678Six or nine digits naming the mailer.
Serial number1234567The shipper's number for this package.
Check digit0A MOD 10 digit computed from the tracking number.
  • Passed34 digits: format C01, a nine-digit Mailer ID and a nine-digit ZIP.
  • PassedCheck digit 0 matches fields 3 to 6.
  • PassedThe nine-digit Mailer ID starts with 9, as it must.
  • Passed123 is in Appendix I, effective 06/24/2026.

Reading the barcode

The tracking number is the part a customer sees: the channel code, Service Type Code, Mailer ID, serial number and check digit. The human-readable text leaves out the routing code and the ZIP Code.

Online, PC Postage and meter barcodes use channel code 94 and add a two-digit source identifier. The source identifier names the kind of online source, such as a PC Postage vendor or a postage meter. USPS assigns each vendor its own source identifier.

The check digit is computed from the tracking number without the routing code and ZIP Code.

The MOD 10 check digit of the tracking number in the specimen.

9212391234567812345670The tracking number with its check digit, 0, at the end.
  1. Add the digits in positions 2, 4, 6 and on, counting from the right: 7 + 5 + 3 + 1 + 7 + 5 + 3 + 1 + 3 + 1 + 9 = 45.
  2. Multiply by 3: 45 × 3 = 135.
  3. Add the digits in positions 3, 5, 7 and on: 6 + 4 + 2 + 8 + 6 + 4 + 2 + 9 + 2 + 2 = 45.
  4. Add the two results: 135 + 45 = 180.
  5. The check digit brings 180 up to a multiple of 10: 0.

Mailer IDs

A Mailer ID is a unique six- or nine-digit number that identifies the mailer or the mailer's client. Customers get Mailer IDs from the Mailer ID tool on the Business Customer Gateway. A six-digit Mailer ID begins with a digit from 0 to 8. A nine-digit Mailer ID begins with 9. A mailing agent assigns a separate Mailer ID to each client.

High-volume shippers and shippers who need longer serial numbers may ask for a six-digit Mailer ID. An online or PC Postage customer with 100,000 pieces or more in six months must use a six-digit Mailer ID.

Service Type Codes

A Service Type Code is a three-digit code that names the mail class and service combination of a package. It differs from the Service Type ID in the Intelligent Mail barcode for letters and flats. The code must match the class, product and services shown on the physical label.

Service Type Codes for the IMpb. Filter them by mail class or extra service.

IMpb Service Type Code List, Appendix I
CodeDescriptionMail classBanner textExtra service codes
001USPS Ground Advantage: Up to 15.999oz USPS TrackingFCUSPS TRACKING #920
019Priority Mail ReturnPMUSPS TRACKING #452
020USPS Ground Advantage Return: Up to 15.999ozFCUSPS TRACKING #452
021USPS Ground Advantage: Up to 15.999oz Signature ConfirmationFCUSPS SIGNATURE TRACKING #921
022USPS Ground Advantage Return: One Pound or MoreFCUSPS TRACKING #452
026Priority Mail: Certified MailPMUSPS CERTIFIED MAIL™910
027Priority Mail: Certified Mail Return ReceiptPMUSPS CERTIFIED MAIL™910, 955
028Priority Mail: Certified Mail Return Receipt ElectronicPMUSPS CERTIFIED MAIL™910, 957
029Priority Mail: Certified Mail Return Receipt Return Receipt ElectronicPMUSPS CERTIFIED MAIL™910, 955, 957
031Priority Mail: Certified Mail Return ReceiptPMUSPS CERTIFIED MAIL™911, 955
032Priority Mail: Certified Mail Restricted DeliveryPMUSPS CERTIFIED MAIL™911
033Priority Mail: CODPMUSPS COD SIGNATURE TRACKING #915
035Priority Mail: COD Return ReceiptPMUSPS COD SIGNATURE TRACKING #915, 955
037Priority Mail Return: Hazardous MaterialsPMUSPS TRACKING # HAZMAT452, 857
039Priority Mail: COD Return Receipt ElectronicPMUSPS COD SIGNATURE TRACKING #915, 957
043USPS Ground Advantage: One Pound or More Registered Mail Restricted Delivery Return ReceiptFCUSPS REGISTERED MAIL™941, 955
046Priority Mail: COD Restricted Delivery, Return Receipt ElectronicPMUSPS COD SIGNATURE TRACKING #917, 957
049Priority Mail: COD Restricted Delivery Return ReceiptPMUSPS COD SIGNATURE TRACKING #917, 955
052Priority Mail: COD Restricted DeliveryPMUSPS COD SIGNATURE TRACKING #917
053Priority Mail: COD Signature ConfirmationPMUSPS COD SIGNATURE TRACKING #915, 921
055Priority Mail: USPS TrackingPMUSPS TRACKING #920
058Priority Mail: Insurance <= $500PMUSPS TRACKING #930
061Priority Mail: Insurance > $500PMUSPS SIGNATURE TRACKING #931
063Priority Mail: Signature Confirmation Hazardous MaterialsPMUSPS SIGNATURE TRKNG # HAZMAT921, 857
065Priority Mail: Insurance > $500 Return ReceiptPMUSPS SIGNATURE TRACKING #931, 955

1 to 25 of 346 codes in the IMpb Service Type Code List, Appendix I.

USPS Tracking Electronic Services Certification

USPS Tracking Electronic Services Certification is the testing and certification process for the Electronic Service option of USPS Tracking. USPS Tracking has two options, Electronic Service and Retail Service. The Electronic Service option gives the shipper the date and time of each item's delivery or attempted delivery. It lets a company build its own mailing profiles and reports from the file USPS sends.

A shipper that chooses the Electronic Service option must complete the certification. A shipper completes label and file certification before it uses the IMpb. Until certification is complete and the Mailer ID is registered, the Mailer ID cannot go in a barcode. The certification checklist serves new customers who want tracking information, and existing customers who convert to the IMpb or add a mail class or extra service. The shippers who should apply send parcels, such as Priority Mail and Parcel Select.

Certification tests the shipper's barcoded labels and electronic file against USPS's specifications, and tests the file's transmission to USPS. The specifications are in Publication 199 and in USPS2000508, the package barcode specification.

The checklist USPS gives shippers that certify.

  1. Create a test Shipping Services File with at least 10 D1 records.
  2. Send the test file to the Product Tracking and Reporting Testing Environment for Mailers.
  3. Review the confirmation/error/warning report that the test environment returns.
  4. Print 10 test labels on each printer.
  5. Send the labels with PS Form 5052 to the Confirmation Services Support Team.
  6. Receive the email that authorizes mailing in the tested mail classes.

USPS provides PS Form 3152, Confirmation Services Certification, when it certifies a shipper's files and barcode samples.

One application form serves this and other certification programs, such as Parcel Return Services.

Applications/Forms

Rules

As part of these efforts, mailers are required to include both an Intelligent Mail package barcode (IMpb) and Intelligent Mail matrix barcode (IMmb) on all parcel types.

Every parcel must carry both the IMpb and the matrix barcode. The one exception is BPM NonPresorted.

In addition to barcode requirements, mailers must also submit an approved electronic file format such as a Shipping Services File (SSF).

Besides the barcodes, a mailer must send an approved electronic file, such as a Shipping Services File.

The Shipping Services File and address information must be transmitted timely and received by the Postal Service before the AAU scan event.

The file and the address must reach USPS before the package's AAU scan. USPS spells AAU out two ways: Arrival at Post Office and Arrival at Unit.

New customers and customers converting to the IMpb must use version 1.6 or higher of the file format.

A shipper starting on the IMpb or converting to it must use Shipping Services File version 1.6 or a later version.

All mailers utilizing the new Intelligent Mail package barcode are required to use a conforming Mailer ID (MID).

Every mailer that uses the IMpb must use a Mailer ID that follows the rules for its first digit.

Mailers may not use a MID in their tracking barcodes for the Shipping Services File or in an IMpb until certification is complete and the MID is registered.

A mailer must not put a Mailer ID in a barcode or a file until certification is complete and the Mailer ID is registered.

The serial number is required to remain unique for 120 days.

A serial number must not repeat on another package for 120 days.

The full tracking number, including the Channel Application Identifier (AI), must be provided to your customer on all communications (i.e. email, receipts, or invoices) so that they can track their packages on the USPS Tracking web site, through the USPS mobile application, or the USPS Tracking API.

A shipper must give its customer the full tracking number, channel code included, in every email, receipt or invoice.

What goes wrong

USPS charges a Package Quality Noncompliance fee when a shipper's noncompliant pieces pass the threshold in any category. Each category has a minimum share of compliant pieces.

CategoryCodeWhat it checksThreshold
Address QualityAQA timely address that validates to a unique 11-digit DPV90%
Manifest QualityMQA timely manifest file that passes critical validation94%
Barcode QualityBQThe barcode in the manifest passes critical validations98%
Hazmat QualityHQThe package has all the correct hazmat elements100%

The thresholds and fees apply to Priority Mail, USPS Ground Advantage, Parcel Select and several other products. The fee is $0.25 per piece. It applies only once to a parcel below the thresholds. The hazmat fee varies by product.

Address and manifest quality use the data in the Shipping Services File, measured at the first AAU scan. Barcode quality is measured at the first physical scan or at receipt of the file. Metered shippers who miss the requirements lose Commercial Pricing and pay retail prices.

The AAU scan is a scan event in scan event extract files.

The scan event that marks the AAU.

PTR Domestic Scan Events, October 2026, 07

Extract description
ARRIVAL AT UNIT
USPS.com wording
Arrived at Post Office
Status category
In Transit
What it means
The item has arrived at the local Post Office on the day indicated and is scheduled for delivery. Usually, if the item arrives before 9:30 am, it will be delivered that day; if after 9:30 am, on the next business day
Starts the clock
No
Stops the clock
No

Barcode Quality failures include:

  • Duplicate tracking numbers on different packages within 120 days.
  • An invalid Mailer ID in the barcode.
  • Wrong use of the service banner, service icon, Service Type Code or indicia.
  • A weight or destination rate that does not fit the Service Type Code.

Paying the fee does not exempt a shipper from the requirements. Parcels without the barcodes and electronic file may be rejected or intercepted.

A shipper reads the confirmation/error/warning file to confirm that no records were rejected as errors.

Terms

Intelligent Mail Package BarcodeIMpb
An IMpb is the USPS-developed barcode that can be read by automated parcel-processing equipment and scanning devices and consists of a data string that generally follows the GS1-128 specification.
Intelligent Mail Matrix BarcodeIMmb
An IMmb is a supplemental GS1-DataMatrix (2D) barcode, which is intended to improve package visibility.
Package Identification CodePIC, Piece Identification Code
A Package Identification Code or PIC is a unique data string that serves as a unique tracking number for a mailpiece. Each PIC will consist of an Application Identifier, service type code, data string that will vary based upon the specific data construct, and a MOD 10 check digit.
Service Type CodeSTC
Service Type Codes are designators used to represent USPS classes of mail in conjunction with the type of Extra Service(s) being requested.
GS1 Application IdentifierAI, Application Identifier
GS1 Application Identifiers are a specific set of defined identifiers used to connect physical and logical things to information or business messages related to them. This field of two or more characters at the beginning of an Element String uniquely defines format and meaning of the string.
Shipping Services FileSSF, Shipping Service Files
The electronic file containing all manifest and payment information.
USPS Tracking
USPS Tracking consists of 2 options: Electronic Service and Retail Service. With both options, mailers receive information about the delivery status of Priority Mail® service or Package Services, including the date, time, and ZIP Code™ of delivery.

Documents

Technical Specifications

Tech Guides

Publications

Fact Sheets

Quick Service Guides

User Guides

FAQs

Presentations

Data Files

Applications/Forms

Contacts

Addressing and Geospatial Technology answers questions about the IMpb by phone at 1-877-264-9693, option 1, or by email at delivery.confirmation@usps.gov. The Package Services Customer Support Team answers Mailer ID questions at the same email address and phone number. The Confirmation Services Support Team answers questions about errors and warnings in a test file at 877-264-9693. Customers who need help with USPS Tracking Electronic Services Certification may call 1-800-238-3150, Monday to Friday, 8:00 am to 5:00 pm CST.

Sources