The Intelligent Mail bar code is a United States postal service bar code for usage with the USPS mail stream.

Intelligent Mail is also known as the USPS OneCode Solution or USPS 4-State Customer Barcode. Valid abbreviations for this bar code type include 4CB, 4-CB, and USPS4CB.

The bar code encodes up to 31 digits. The code value is expected as two comma-separated fields. Each field consists solely of digits. The first field contains the tracking code. The second field contains the routing code.

The encoding is illustrated in the following table. There can be a total of 31 digits maximum.
Table 1. Encoding for the Intelligent Mail bar code
Type Field Digits
Tracking code field Barcode Identifier 2 digits; 2nd digit must be 0-4.
Tracking code field Service Type Identifier 3 digits.
Tracking code field Mailer Identifier 6 or 9 digits.
Tracking code field Serial Number 9 digits, when used with a 6-digit Mailer Identifier.

6 digits, when used with a 9-digit Mailer Identifier.

Routing code field Delivery Point ZIP Code 0, 5, 9, or 11 digits.