The Intelligent Mail barcode (IMb), also known as the USPS OneCode Solution or USPS 4-State Customer Barcode (sometimes abbreviated as 4CB, 4-CB, or USPS4CB) was designed for the United States Postal Service and combines techniques from their previous symbologies — POSTNET and PLANET — to include more information and enhanced tracking data. It is a fixed, 65-bar code that came into use in 2013 and is now required for any type of sorting and delivery automation. It encodes only numeric characters 0-9.
Along with the IMb, the USPS developed parallel symbologies for other specific purposes. For example, the Intelligent Mail package barcode (IMpb) uses GS-128 symbology for enhanced package processing, while the Intelligent Mail tray label uses ISS Code 28 symbology to track all trays, tubs, and mail sacks. Finally, the Intelligent Mail container barcode is scanned at specific processing and transportation points for mailer-generated container labels.
Unlike most barcodes, the IMb doesn’t rely on varying bar and space widths. Instead, this code uses varying “states” to encode information:
Each character in Intelligent Mail codes is made up of four bars, each of which can be in one of four states:
Full bar — This state runs the entire height of the barcode.
Tracker — This state occupies only the middle third of the barcode.
Ascender — This state covers the top two-thirds of the barcode.
Descender — This state covers the bottom two-thirds of the barcode.
By leveraging position rather than width as a primary encoding characteristic, barcode information density is significantly increased, allowing USPS to add more detailed information about package origin, destination, service type, and tracking.
This code contains five key elements:
A leading quiet zone, which must be at least 0.125 inches wide.
The 20-digit tracking code which includes these potential fields:
A Barcode Identifier (2 Digits)
The Service Type Identifier (3 Digits)
Mailer ID (6 or 9 Digits)
Origin Customer Tracking Number
Mail Processing Type and Equipment Number
Serial or Sequence Numbers (6 or 9 Digits)
A routing code which includes the delivery ZIP code. This code may be omitted, in which case it is 0 characters. Otherwise, it is 5, 9, or 11 digits long.
A trailing quiet zone.
The IMb also requires top and bottom quiet zones of 0.028 inches, and can only be used on letter-sized or flat mail. To ensure accurate reading, the code must be placed either above or below the destination address within the address block, above the address block itself, or in a designated barcode “clear zone.” It must also be printed at zero degrees.
Common Use Cases
This code was adopted by the USPS as a way to combine the encoding abilities and symbologies of its two previous barcode iterations, POSTNET and PLANET. Similar to Australia’s four-state code, the IMb offers significantly improved information density and security while also enhancing the ability of USPS facilities to automate the sorting, tracking, and delivery process.