CASS Certification
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Coding Accuracy Support System — a USPS program that certifies address-matching software to ensure it assigns correct ZIP+4 codes and delivery point codes.
CASS (Coding Accuracy Support System) is a USPS testing and certification program for software that standardizes addresses and assigns ZIP+4 codes. Software vendors submit their products to USPS testing on a regular cycle, and certified software receives a CASS certification ID valid for a limited period (typically one year).
Mailers must process their address lists through CASS-certified software to qualify for USPS automation postage discounts. The CASS process standardizes address components (street suffix, directional, secondary designator), appends the ZIP+4 code, and flags addresses it cannot match to the USPS database as undeliverable.
CASS-certified processing also generates a USPS Form 3553 (Certification Statement) that documents the address quality of a mailing and must be submitted with the mailpiece to claim discounts.