USPS Intelligent Mail Barcode Decoder
What is a USPS Intelligent Mail Barcode?
The USPS Intelligent Mail Barcode (IMb) is a 65-bar barcode printed on First-Class and Standard mail pieces. It replaced the older POSTNET and PLANET barcodes and became the USPS standard for automation-compatible mail.
Every IMb encodes a digit string — typically printed in small text directly below the barcode — that identifies the mailer, the individual mail piece, and optionally the delivery address. USPS scanners at processing facilities and delivery units read these barcodes and generate events in the Informed Visibility system, which tracks the movement of mail through the postal network.
IMb digit string structure
| Field | Digits | Description |
|---|---|---|
| Barcode ID | 2 | Identifies the type of mail piece and presort level. Common values: 00 (Default), 04 (Letter), 70 (Flat). |
| Service Type ID | 3 | Encodes the class of mail and any special services (e.g. address correction, return service). 040 = First-Class Mail, no extra services. |
| Mailer ID | 6 or 9 | USPS-assigned identifier for the organization that generated the barcode. 6-digit MIDs for large mailers, 9-digit for smaller mailers. |
| Sequence Number | up to 10 | Mailer-assigned number uniquely identifying each mail piece within the MID. Must be unique for 45 days. |
| Routing Code | 0, 5, 9, or 11 | Optional delivery point. 5 digits = zip5, 9 digits = zip+4, 11 digits = delivery point barcode (DPBC). |
Common Service Type Identifiers
| STID | Class | Services |
|---|---|---|
| 040 | First-Class Mail | No extra services |
| 044 | First-Class Mail | Address Service Requested |
| 261 | Standard Mail | No extra services |
| 300 | Periodicals | No extra services |
| 401 | Parcel Select | No extra services |
What the Mailer ID tells you
The Mailer ID identifies who generated the barcode — not necessarily who sent the mail piece. Commercial mailers, mailing service providers, and software platforms each have their own MID. If you see an unfamiliar MID on a piece of mail, it may reflect the software or service that generated the barcode rather than the sender's company name.
USPS does not provide a public lookup for Mailer IDs — they are assigned through the USPS Business Customer Gateway and are not published in a searchable directory.
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