CASS

CASS stands for Coding Accuracy Support System. It is the USPS program that certifies address-matching software — and by extension, the addresses that software produces — as standardized to the format USPS sortation infrastructure can read. A CASS-certified address has been parsed, normalized, validated against the official USPS address database, and tagged with a ZIP+4 code and a two-digit delivery-point code that together uniquely identify a single mailbox. A list that has cleared CASS qualifies for automation postage rates. A list that has not, doesn’t.

Where it came from

USPS launched CASS in 1990. The motivation was the same as NCOA’s: cost. The Postal Service was rolling out automated optical-character-recognition sortation, and a meaningful portion of mail couldn’t be machine-read because addresses arrived in dozens of inconsistent formats — “Street” vs “St.” vs “ST”, suite numbers in five different positions, ZIP codes that didn’t match the city. CASS was the certification framework that pushed standardization upstream, to the mailer’s software, before the piece ever entered the mail stream. The CASS spec is updated annually; software vendors recertify every USPS Cycle (the current cadence is Cycle O), and a certification that lapses can’t be used to qualify mail for automation rates.

How it actually works

A CASS-certified processor takes a raw input address — whatever format it arrived in — and runs it through a four-step pipeline. First, parse: split the input into recognized components (primary number, street name, suite, city, state, ZIP). Second, standardize: apply USPS abbreviations and conventions (Avenue becomes AVE, North becomes N, Apartment becomes APT). Third, match: look the standardized address up in the USPS Address Information System (AIS) database, which is the canonical record of every deliverable address in the United States. Fourth, code: append the matched ZIP+4 and the two-digit delivery-point code (DPC), producing the eleven-digit identifier USPS sortation actually uses. The output is a CASS-certified record — with the original input, the standardized output, and a status code documenting what kind of match happened.

The match codes matter. A clean CASS hit is what most lists return on most records. But CASS can also return ambiguous matches (multiple AIS records fit the input), no-match (the input doesn’t correspond to any deliverable address), and rural-route or PO-Box cases that have their own handling rules. The USPS Form 3553 — the document USPS requires alongside the manifest to qualify mail for automation rates — reports the breakdown of these codes for the drop, which is why most platforms surface CASS results in a per-drop report.

What goes in, what comes out

Input: a list of addresses in any format — cleanly formatted or not, with or without ZIP+4. Output: the same list with each address standardized to USPS format, ZIP+4 and delivery-point code appended, and a match-code disposition per record. Records that don’t match the AIS database at all are flagged for review, not silently passed through — an unmatched record is almost always a typo or a non-deliverable address, and the right response is to fix the source data, not to mail to it. CASS does not check whether the address is currently occupied or whether the recipient still lives there — that is the job of NCOA and DPV. CASS only certifies the address itself is real and properly formatted.

Common pitfalls

The first pitfall is treating CASS as a one-time cleanup. The AIS database changes — new construction, renamed streets, ZIP+4 reassignments — and a CASS pass run six months ago may produce different output than one run today. USPS requires CASS to be re-run if the list ages out of the certification window. The second pitfall is conflating CASS with NCOA. CASS standardizes the address; NCOA updates it for moves. They run in sequence on every list, and skipping either disqualifies the drop from automation rates. The third pitfall is ignoring the unmatched records. Most teams default to dropping no-match addresses, which is correct, but the upstream question — why is this data source producing so many unmatched records? — is the one that protects future drops. Lists with high CASS-fail rates almost always trace to a scraped or self-reported data source that was never validated at intake.

How DirectMail.io runs it

CASS runs on every list, every drop, in sequence with NCOA and DPV before press queue. The Form 3553 documentation is generated automatically and rides with the USPS manifest. Match-code dispositions are surfaced in the dashboard so the team can see exactly which records standardized cleanly, which were ambiguous, and which failed — and route them to the right next step. Details are on the CASS feature page.

When to use this

• Before any presorted drop. Automation rates are conditional on CASS certification within the current window. Without CASS, the drop pays full retail postage.
• On any list arriving from outside. Client uploads, data partner files, and form-collected addresses all arrive in inconsistent formats. CASS at ingest is the first chance to catch typos and bad records before they reach the press.
• As a quality signal on the data source. If a source consistently returns high CASS-fail rates, the source has a data-quality problem worth fixing upstream.

For the broader hygiene workflow CASS sits inside, see the seven-step list-hygiene checklist.