UNITED STATES POSTAL SERVICE ZIP+4 GUIDELINES - 5180

The USPS offers a reduced postage rate to organizations for first-class mailings that use the 9-digit zip code (ZIP +4) in the mailing address. Both unsorted and sorted mailings are eligible for the reduced rate.

To the extent that it is cost-effective (taking into account the potential postage discount), agencies must provide for ZIP + 4 address coding and sorting of printed addresses in ZIP + 4 order in the design and operation of automated information systems that include preparation of mailing addresses.

There are two preliminary requirements for eligibility for the ZIP + 4 discount;

1. "Machinability," which includes quality of paper stock and adherence to the USPS standards for envelope size; and,
2. Optical Character Recognition (OCR) readability, which consists of adherence to the USPS OCR mailing guidelines.

Detailed specifications for these and other ZIP + 4 requirements are available from the USPS Commercial Account Representative assigned to each agency. Additional information is also contained in Section 324 of the USPS Domestic Mail Manual.