Topic 05 of 07
CASS certification
USPS Coding Accuracy Support System—software certification and a process that improves ZIP+4 and delivery-point accuracy for US mail.
Why it matters
CASS-certified processing is often required (or strongly rewarded) for US bulk mailing discounts and is a practical quality bar for deliverable US addresses.
What CASS is
CASS is a USPS program that tests address-matching software against sample files. Certified engines assign ZIP+4 codes and related delivery attributes more accurately.
When vendors say they are “CASS certified,” they mean their matching software passed USPS testing—not that every individual address you send them is magically perfect forever.
What you get from CASS processing
Standardized address components, ZIP+4, delivery point codes, and footnotes explaining corrections or failures.
Outputs support Form 3553 (CASS Summary Report) documentation used with mailing permits and postage discounts.
Limits to know
CASS focuses on USPS deliverability coding—not international addresses, and not full change-of-address updates (that is NCOA’s role).
New construction and rapidly changing areas can lag reference files. Plan for exception handling.
Related topics
- Address verification→
Confirm that an address exists in authoritative reference data and can typically receive mail or deliveries.
- NCOA — National Change of Address→
USPS-licensed process that updates addresses when people and businesses file official change-of-address moves.
- Standardization & formatting→
Rewrite addresses into a consistent, preferred format so systems can compare, store, and print them reliably.