What Is CASS-Certified Software?
Firstlogic Team
CASS-certified software is address-matching software that the United States Postal Service has tested under the Coding Accuracy Support System (CASS). In plain terms: the Postal Service runs the product against a standard test file, scores how accurately it assigns postal codes, and - if the product passes - lists it as certified.
The important word in that sentence is software. CASS certifies the product - not your mailing list, not your customer database. The USPS test says "this engine can code addresses correctly." It does not say "every address in your file is correct." If your file has misspellings, outdated street names, or missing apartment numbers, the software will still do its best, but no certification score guarantees the output. Results on a real list always depend on the quality of the addresses you feed in.
That distinction is what most people are looking for when they search for "CASS certification" or "CASS-certified software" - especially if they are buying or licensing address software for mail preparation, data quality, or operations.
What CASS certification actually measures
According to USPS PostalPro, CASS gives hardware and software developers, service bureaus, and commercial mailers a shared way to test address-matching software. The Postal Service's Addressing and Geospatial Technology office grades the tests and returns results so developers can fix gaps.
There is a practical reason to care. Any mailing claimed at an automation price - the discounted postage rates that depend on accurate barcoding and sortation - must be produced from address lists matched and coded with CASS-certified methods. Without that, the mailing may not qualify for those rates.
The certification test has two stages:
- Stage I is optional. Developers get a self-test file of about 150,000 addresses, with answers, so they can debug before submitting for a real score.
- Stage II is required. It uses a similar file without answers. The vendor processes it and returns the results for USPS scoring.
To pass, PostalPro currently requires at least 98.5 percent accuracy for ZIP+4, carrier route, five-digit ZIP, and LACSLink, and 100 percent for delivery point coding, eLOT, DPV or DSF2, RDI, and Perfect Address.
In practice, that means the software is evaluated across the coding jobs mailers rely on: five-digit ZIP, ZIP+4 and delivery point, carrier route, and supporting products such as DPV or DSF2 (delivery-point checks), LACSLink (updated addresses after 911-style renumbering), SuiteLink (missing business suite numbers), eLOT (approximate carrier line-of-travel order), and RDI (residential versus business delivery).
What the software does with a live list
Once certified software is in production, it is the engine that takes a U.S. address, standardizes the wording to Postal Service format, and assigns the codes needed for automation mail and barcoding. Typical outputs include ZIP+4, carrier route, delivery point, and the supporting indicators listed above.
That production work also feeds PS Form 3553, the CASS Summary Report. Mailers submit that report when they claim automation discounts. Firstlogic Address IQ, for example, produces Form 3553 as part of its job reports.
What CASS-certified software does not do on its own is also worth stating clearly:
- It will not tell you that a person or business has moved. That is the job of NCOA (National Change of Address).
- It will not invent a mailbox on a vacant lot. DPV can flag that a primary number is not a known delivery point; it does not create one.
What the software does in production
Certification is not permanent. Generally, CASS-certified software stays certified until the end of the current CASS cycle. When that cycle ends, the product has to pass Stage II again for the next cycle. Mailings produced from uncertified software are not eligible for USPS automation prices.
That is the binding rule in the Domestic Mail Manual (section 509.1.7): the Postal Service certifies software that meets its standards until the applicable CASS cycle expires, and software must be re-certified for each CASS cycle. For a mailer or operations team, that means a product that passed Stage II for Cycle O remains certified through the end of Cycle O, unless the software itself changes in a way that requires a new test.
A CASS cycle is the program framework the Postal Service uses for matching rules, data products, and file formats. When a new cycle starts, vendors implement those changes and recertify. Cycles are not locked to a two-year calendar. Their length has varied with Postal Service modernization and industry readiness. Cycle O is the current cycle. It took effect in August 2023, and PostalPro lists Cycle O certified-product guides as expiring July 31, 2028. Firstlogic announced CASS Cycle O certification for Address IQ on April 20, 2023.
Some businesses have to maintain and renew CASS certification for their software more frequently than once per cycle. Under the USPS terms for CASS software developers, a significant update to certified software or its configuration requires recertification and a new Stage II test before that release can be used as CASS-certified. If you are evaluating a vendor, ask which CASS cycle the product holds, when that cycle's certified-product listing expires, and whether the current release has passed Stage II after any material software change.
CASS is not NCOA
CASS and NCOA often appear together in RFPs and vendor questionnaires, which makes it easy to treat them as interchangeable. They solve different problems.
CASS asks whether the software can code addresses to Postal Service standards. NCOA asks whether the person or business at that address has filed a move. You can have perfectly coded addresses for people who no longer live there, and you can have current occupants at addresses that still need standardization. For a fuller side-by-side, see CASS vs NCOA.
Why operations teams license certified software
In January 2026, USPS retired its older Web Tools APIs - the public interfaces many teams had used for online address lookups. Replacement REST APIs remain available for validating addresses over the web. Like other cloud APIs, they are subject to usage limits, which some organizations weigh when they process large files on a schedule. That is one of several reasons a large organization might choose self-managed, licensed software over a web API or cloud service - including the ability to run CASS-certified processing in-house and produce Form 3553 for automation postage. The 2026 change is covered in more detail in USPS API changes in 2026.
Firstlogic Address IQ is self-managed CASS Cycle O software for U.S. address cleansing. You can try a sample in the verify-address demo, or read the certifications notes and the Address IQ product page.
Frequently asked questions
What is CASS certification?
What does CASS-certified software do?
How long is CASS certification good for?
How is CASS different from NCOA?
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