IMB Barcode Requirements: 2026 USPS Intelligent Mail Barcode Guide

The IMB barcode requirements for 2026 come down to five numeric fields and one print specification. The Intelligent Mail barcode (IMB) carries a 2-digit Barcode Identifier, a 3-digit Service Type Identifier, a 6- or 9-digit Mailer ID, a 6- or 9-digit Serial Number and a Routing Code of 0, 5, 9 or 11 digits, printed as 65 bars between 2.667 and 3.225 inches wide. Letters, cards and flats need a valid IMB to earn USPS automation prices, and Full-Service mailings add a unique Serial Number on every piece plus electronic documentation.

MPA encodes the IMB on the presorted letters, cards and flats we mail, and the sections below follow the order we check a job in: the fields, the print specification, Full-Service, then what an error costs.

What Is an IMB Code?

An IMB code is the same thing as the Intelligent Mail barcode: the 65-bar symbol USPS reads to route, sort, and track letters, cards, and flats. Mailers and presort software use the labels interchangeably (USPS itself writes IMb), so "IMB code," "IMB barcode," and "Intelligent Mail barcode" all describe the same payload of up to 31 digits and the same physical specification.

The format carries several legacy names that still appear in vendor documentation and software menus. USPS introduced it as the OneCode Solution, because one symbol replaced the two barcodes mailers previously had to print. It is also called the 4-State Customer Barcode, abbreviated 4CB or USPS4CB, after the four bar states (full, ascender, descender, and tracker) that encode the data. It superseded POSTNET, which held only routing digits, and PLANET, which held only tracking digits. A single IMB code now does both jobs, which is why one scan can return a delivery point and a piece-level tracking event together.

One distinction matters when you look up specifications: the IMB covers letters, cards, and flats, while parcels use the separate Intelligent Mail package barcode (IMpb), which has its own field structure and tolerances. Our breakdown of IMpb versus IMB covers that split if a campaign mails both. USPS publishes the authoritative field definitions and the free Encoder/Decoder tool at Intelligent Mail Barcode (PostalPro, USPS).

Encoding the code correctly is what moves a mailing onto automation pricing. MPA builds the IMB in house as part of presort mailing services, so the barcode, the presort depth, and the eDoc submission all come out of one workflow.

The Five Required IMB Fields

The first four fields form a 20-digit tracking code that identifies the presort level, the mail class and services, the sender and the individual piece. The fifth, the Routing Code, adds 0, 5, 9 or 11 digits of destination ZIP Code, so every valid IMB holds between 20 and 31 digits before it is converted into bars. Here is one decoded, using illustrative values rather than a live Mailer ID:

Strung together, the 31 digits read 00 270 123456 000012345 12345678901 (spaces added for reading). Presort software or the USPS Encoder turns a string like this into the 65-bar symbol.

1. Barcode Identifier (2 digits)

The Barcode Identifier is reserved for the presort level that is printed in readable form on the optional endorsement line (OEL), the line of asterisks and sort level above the address on many presorted pieces. USPS says to leave it at 00 when no OEL is printed. Automation flats that print an OEL must encode the matching sort level: 10 for carrier route, enhanced carrier route or FIRM; 20 for 5-Digit or 5-Digit scheme; 30 for 3-Digit or 3-Digit scheme; 40 for ADC; and 50 for Mixed ADC or origin mixed ADC.

The second digit is always 0 through 4, so a value such as 05 or 57 is never valid. USPS lists the codes on its Barcode Identifier sheet (PostalPro).

2. Service Type Identifier (3 digits)

The Service Type Identifier (STID) tells USPS the mail class, whether the piece is mailed under the Basic or the Full-Service option, which address correction service the mailer wants, and whether piece scan data should flow to the mailer through Informed Visibility Mail Tracking & Reporting (IV-MTR). USPS publishes every value in the STID table on PostalPro. The codes are stable: USPS revises the table when it adds or retires a service option, not at each price change. These are the values for mail that requests no address correction:

Address correction options (OneCode ACS, Full-Service ACS and Traditional ACS, each paired with an endorsement such as Address Service Requested or Change Service Requested) have their own STIDs in the same table. On a Full-Service mailing, USPS compares the STID in each barcode with the class and services claimed in the electronic documentation, and a mismatch counts as a Full-Service STID error.

3. Mailer ID (6 or 9 digits)

The Mailer ID (MID) is a number USPS assigns to identify the mail owner or the mail preparer. High-volume mailers receive 6-digit MIDs; everyone else receives 9-digit MIDs. The first digit tells them apart: every 6-digit MID starts with 0 through 8, and every 9-digit MID starts with 9.

One company can hold several MIDs, for example one per business unit, or one as mail owner and another as mail preparer. MPA holds its own MID and can encode customer mail under it when a customer prefers not to obtain one; the electronic documentation still identifies the customer as the mail owner.

4. Serial Number (6 or 9 digits)

The Serial Number identifies the individual piece. Its length mirrors the MID: a 6-digit MID pairs with a 9-digit Serial Number and a 9-digit MID with a 6-digit one, so the STID, MID and Serial Number always total 18 digits. Add the 2-digit Barcode Identifier and you have the 20-digit tracking code.

Under Full-Service, a Serial Number may not repeat within 45 days for the same MID, so every IMB stays unique for that window. A repeat counts as a Full-Service uniqueness error on the Mailer Scorecard. It does not void the mailing; errors above the USPS threshold lead to an assessment, covered in the Full-Service section below.

5. Routing Code (0, 5, 9 or 11 digits)

The Routing Code is the destination: empty, a 5-digit ZIP Code, a 9-digit ZIP+4, or an 11-digit delivery point code (ZIP+4 plus two delivery point digits). Automation letters must carry the 11-digit delivery point routing code, which comes from matching each address with CASS-certified software. USPS uses that code to sort letters into each carrier's delivery order.

In MPA production data, about 94% of records on a typical consumer list pass CASS/DPV address validation, and about 98.5% of those validated records are deliverable after NCOA processing. We run every list through CASS and NCOA processing before encoding, so the routing codes match current addresses.

IMB Print Specifications and Placement

The other half of the requirements is physical. USPS barcode sorters read the bars by height, so size, clear space and position all matter. The figures below come from the USPS barcode specification (USPS-B-3200) and Domestic Mail Manual section 202:

Print the IMB from the USPS IMb font or certified software at its native size. Stretching or shrinking it in a layout program changes the bar widths and spacing, and the width can fall outside tolerance.

On an automation letter, the IMB with its delivery point routing code goes either in the address block (for example above the recipient's name line or below the city, state and ZIP Code line) or inside the barcode clear zone. A letter that carries that barcode in the address block does not need a barcode clear zone; on any other automation letter, the clear zone must hold nothing but the IMB itself. On a window envelope, keep the same clear space between the barcode and the window edges in every position the insert can shift to (DMM 202, section 5).

The Two Most Common Print Errors

These are the two IMB problems we see most often in customer-supplied print files:

• A resized barcode. Someone scales the IMB to fit a space in the layout, which distorts the bars or pushes the width outside 2.667 to 3.225 inches. Fix: place it at its native rendered size and size the space around the barcode instead.
• Printing in the clear space or the clear zone. An indicia, an endorsement line, a logo or a background tint runs into the clear space around the bars, or into the barcode clear zone on a letter that needs it blank. Fix: build both areas into the template as no-print zones.

Either error can leave USPS equipment unable to read the barcode, and a piece it cannot read does not qualify for the automation price.

Full-Service IMB Requirements

Full-Service is the USPS option that adds piece-level documentation and tracking on top of automation. A Full-Service mailing needs:

• A unique IMB on every piece. Every piece, not a sample, carries an IMB with a Full-Service STID and a Serial Number that does not repeat within 45 days.
• Intelligent Mail tray barcodes (IMtb) on every tray and sack, each unique.
• Intelligent Mail container barcodes (IMcb) on every pallet or other container, each unique.
• Electronic documentation (eDoc) submitted through PostalOne!, such as a Mail.dat file, that links each piece barcode to its tray, container and postage statement. A hardcopy postage statement does not qualify.
• The mail owner and mail preparer identified in that documentation (the By/For fields), by MID or CRID.

In return, each Full-Service piece earns the Full-Service discount (half a cent per piece on First-Class automation letters and cards and on Marketing Mail automation letters in the current Notice 123), free electronic address corrections through Full-Service ACS, and start-the-clock data showing when USPS accepted the mail. Piece scan data through IV-MTR is available to Basic mail too, through the STIDs above.

How USPS Enforces Full-Service

USPS checks Full-Service mail electronically against the eDoc and posts the results to the Mailer Scorecard. The checks cover the MID, the STID, the mail owner and preparer fields, barcode uniqueness, the entry facility and unlinked co-palletization. When errors in a category exceed the USPS threshold for a calendar month, USPS generates an assessment at the CRID that submitted the eDoc. The assessment removes the Full-Service discount from the pieces in error above the threshold; it does not reprice the rest of the mailing (Full-Service assessments, PostalPro).

2026 Automation Prices by Mail Class

The IMB has no price of its own, but the class and sort it supports do. These are USPS Notice 123 automation prices at the Mixed tier, in effect since July 12, 2026, before the Full-Service discount, with the Full-Service STIDs for mail that requests no address correction:

3-Digit and 5-Digit sorts price lower than Mixed. Source: USPS Notice 123 (Price List); our 2026 USPS postage rates page carries the full price tables.

What a Barcode Error Actually Costs

An IMB error costs the affected pieces, not the whole mailing. A presorted piece whose barcode cannot be read, or that misses the automation standards, is not eligible for the automation price and qualifies only for the nonautomation machinable price of its class. At the Mixed tier that gap is small, under two cents per piece for First-Class letters and cards and for Marketing Mail letters in the current Notice 123.

The expensive case is a piece pulled from the mailing and sent on its own at retail: a single-piece retail First-Class letter is $0.82 against the $0.707 automation Mixed price, about 16% more, and a single-piece retail postcard is $0.65 against $0.495, about 31% more. USPS Marketing Mail has no single-piece price at all; it exists only as presorted commercial mail.

Full-Service documentation errors cost less. An assessment removes only the per-piece Full-Service discount from the pieces in error above the threshold, and the automation price on those pieces stands.

How MPA Handles IMB Encoding

For customers who would rather not manage MIDs, Serial Number registries and eDoc in house, MPA runs the whole chain:

Address hygiene. Every list runs through CASS and NCOA before any barcode is encoded, so the routing codes match current, deliverable addresses.

MID and STID. We encode under our MID or yours, and choose the STID that matches the mail class and the address correction and tracking services you want.

Serial Number registry. We track Serial Numbers per MID so no IMB repeats inside the 45-day Full-Service window, across every job we mail.

Print. The IMB is printed at native size, with the clear space and the barcode clear zone built into our templates.

eDoc and entry. Every Full-Service mailing goes to USPS with a Mail.dat file through PostalOne! that links each barcode to its tray, container and postage statement. We enter the mail under our own USPS mailing permit at the Lakeland BMEU, and can also enter at the Tampa P&DC or the Mid-Florida P&DC.

Our team works from one Lakeland, Florida facility and mails for businesses in all 50 states. Every quote is itemized, with postage on its own line. If IMB compliance is slowing your team down, talk to us about our mailing services.

Frequently Asked Questions

What are the IMB barcode requirements for 2026?

Five numeric fields (a 2-digit Barcode Identifier, a 3-digit Service Type Identifier, a 6- or 9-digit Mailer ID, a 6- or 9-digit Serial Number and a 0-, 5-, 9- or 11-digit Routing Code) printed as a 65-bar code 2.667 to 3.225 inches wide with full bars 0.125 to 0.165 inch tall, clear space around it, and correct placement on the piece. Full-Service mailings also need a Serial Number that does not repeat within 45 days, tray and container barcodes, and electronic documentation submitted through PostalOne!

What are the 5 fields of an IMB?

The Barcode Identifier (2 digits: the presort level printed on the optional endorsement line, or 00 when there is none), the Service Type Identifier (3 digits: mail class, Basic or Full-Service, and the address correction and tracking services), the Mailer ID (6 or 9 digits: the mail owner or preparer), the Serial Number (6 or 9 digits: the individual piece) and the Routing Code (0, 5, 9 or 11 digits: the destination ZIP Code). The first four make a 20-digit tracking code; the Routing Code brings the maximum to 31 digits.

How wide is an IMB barcode?

2.667 to 3.225 inches wide, with full bars 0.125 to 0.165 inch tall. Print it from the USPS IMb font or certified software at its native size; scaling it after rendering distorts the bars and can push it outside tolerance.

Do I need a Mailer ID (MID) to use an IMB?

Yes. Every IMB carries a Mailer ID assigned by USPS. High-volume mailers receive 6-digit MIDs, and everyone else receives 9-digit MIDs, which always start with 9. If you do not want your own, a mail service provider can encode your mail under its MID; MPA does this for customers who prefer it.

What is Full-Service IMB and why does it matter?

Full-Service is the USPS option that requires a unique IMB on every piece (no repeat within 45 days), unique tray and container barcodes, and electronic documentation through PostalOne! that identifies the mail owner and preparer. In return, each piece earns the Full-Service discount off the automation price, free address corrections through Full-Service ACS, and start-the-clock data showing when USPS accepted the mail.

How is the IMB different from the older POSTNET barcode?

POSTNET carried only routing digits (a ZIP Code, ZIP+4 or 11-digit delivery point code) in two bar heights, five bars per digit. The IMB uses four bar states to carry up to 31 digits: the same routing data plus a Barcode Identifier, Service Type Identifier, Mailer ID and Serial Number. Since January 2013, only the IMB qualifies mail for automation prices.

What happens if my IMB is encoded incorrectly?

It depends on the error. A barcode USPS cannot read, or an automation letter without a valid delivery point routing code, makes that piece ineligible for the automation price, so it qualifies only for the nonautomation price of its class. Errors that only Full-Service checks catch, such as a wrong STID, an invalid MID or a Serial Number repeated within 45 days, count on the Mailer Scorecard; when a category exceeds the USPS threshold for the month, USPS assesses the Full-Service discount back on the pieces in error above that threshold. Losing Full-Service credit removes the per-piece Full-Service discount; it does not reprice the drop at single-piece rates.

Can I generate my own IMB or do I need software?

For a small one-off mailing, the free USPS Encoder and IMb font on PostalPro will produce a valid barcode. Recurring presorted mail needs presort software certified under the USPS PAVE program to manage MIDs, Serial Number uniqueness, eDoc and PostalOne! submission. MPA runs that software as part of mail prep for every job we mail.

What is an IMB code?

An IMB code is the Intelligent Mail barcode: a 65-bar USPS symbol that encodes up to 31 digits across five fields so one code handles both routing and piece-level tracking. The terms IMB code, IMB barcode, and Intelligent Mail barcode mean the same thing. USPS first released it as the OneCode Solution, and some presort software still labels it the 4-State Customer Barcode (4CB or USPS4CB).

Is an IMB code the same as an IMpb?

No. An IMB code goes on letters, cards, and flats, while the Intelligent Mail package barcode (IMpb) goes on parcels and uses a different field structure and physical specification. A campaign that mails both letters and parcels needs both barcode types, each built to its own spec.

Bottom Line on IMB Barcode Requirements

The rules have not changed structurally in years: five fields, a fixed print specification, and, for Full-Service, a unique Serial Number per piece plus eDoc. Get them right and every piece qualifies for the automation price the mailing was planned on. Get one wrong and the cost lands on the affected pieces: the nonautomation price for a piece USPS cannot read, or an assessment of the Full-Service discount for a documentation error.

MPA is SOC 2 Type 2 audited on the data side of the workflow and holds a 5.0 star rating across 100+ verified Google reviews. Request a quote for your next mailing and we will price the presort, the IMB encoding and the eDoc, with postage on its own line.