CASS Certification: What It Is and Why Your Mailing List Needs It

A CASS-certified list is the postal-grade version of your mailing data. Run a file through USPS-certified address-matching software and every address comes back corrected to official postal format, carrying its full ZIP+4, and checked against Delivery Point Validation to confirm the delivery point is real. That output is the baseline USPS requires before it will grant automation postage discounts.

If you mail in volume, CASS is not optional. It turns a messy spreadsheet into a file the post office accepts at automation pricing, and it is the difference between mail that lands and mail that comes back undeliverable. This guide covers what CASS does component by component, how software earns certification under the current cycle, how to read a DPV report, how CASS differs from NCOA, and the two real paths to getting a certified file.

What Is CASS Certification?

CASS certification is a U.S. Postal Service program that tests and approves address-matching software, not mailing lists. A list becomes "CASS certified" only by being run through one of those approved engines, which corrects each address to official USPS format, appends the full ZIP+4, and confirms the delivery point exists via Delivery Point Validation. USPS requires that output before it will grant automation postage discounts, and treats the coding as current for 180 days from the processing date.

Official reference: USPS CASS certification program (postalpro.usps.com).

In the files our team processes, approximately 94% of records pass address validation (CASS/DPV) on a typical B2C list. That is the practical payoff of a CASS pass: fewer undeliverables, and a file that qualifies for automation pricing. The processing also produces the CASS Summary Report (PS Form 3553), the document the post office looks for as evidence the addresses were coded by certified software when you claim automation rates on a postage statement.

What CASS Is

CASS stands for Coding Accuracy Support System. It is a certification program operated by the USPS National Customer Support Center that evaluates how accurately a software product matches, corrects, and codes mailing addresses against the official USPS address database.

The key point is that CASS certifies the software, not the list. A vendor's address-processing engine passes a USPS test file at a required accuracy threshold to earn certification for a cycle. When you "CASS a list," you run your addresses through that certified engine, and USPS recognizes the standardized, coded, validated output as certified-software output, which is what makes it eligible for automation pricing.

What a CASS-Certified List Means

A CASS-certified list is one processed through certified software so that every record meets USPS delivery standards. Concretely, a CASS-certified file has three guarantees baked in:

• Every address is standardized to USPS format. Abbreviations, directionals, suffixes, and unit designators are all corrected to the official postal spelling.
• Every deliverable address carries its full ZIP+4. The nine-digit code that pinpoints the delivery point is appended, which is what automation discounts are built on.
• Deliverability is confirmed. Delivery Point Validation has checked each address against real USPS delivery points, so undeliverable records are flagged before they cost you postage.

That is the difference between a raw list and a CASS-certified one: the raw list is what you typed, imported, or rented; the certified list is what the post office delivers against at automation pricing.

What CASS Does, Component by Component

Address Standardization

Address standardization rewrites every record into the exact format USPS publishes in Publication 28, Postal Addressing Standards: it corrects spelling, applies standard abbreviations, fixes directionals, and normalizes unit designators. A messy record like 123 main street apartment 4, lakeland florida 33801 becomes the standardized USPS form 123 MAIN ST APT 4, LAKELAND FL 33801, with the correct ZIP+4 add-on for that delivery point appended at the coding step.

STREET becomes ST, APARTMENT becomes APT, the state spells down to its two-letter code, and the record is now in the precise shape USPS automation equipment expects. Publication 28 is the authority behind every one of those substitutions, which is why two certified engines will produce the same standardized output from the same input.

ZIP+4 Coding

The five-digit ZIP gets you to a post office. The four-digit add-on gets you to a specific block face, building, or single delivery point. CASS appends the full ZIP+4 to every deliverable address. This nine-digit code is the foundation of automation pricing, because USPS gives its automation rates to mail coded and barcoded to the ZIP+4 level, which it sorts by machine with almost no manual handling.

DPV (Delivery Point Validation)

Address standardization and ZIP+4 coding can make an address look perfect even when it does not exist. DPV is the safeguard. Delivery Point Validation checks each address against USPS data on actual delivery points, catching a correctly formatted "999 Main St" that was never built, or an apartment number that is missing or wrong.

DPV returns a single-character confirmation indicator on every record. If you are holding a DPV report from a vendor, these are the codes you are reading:

DPV code	What it means	What to do
Y	Confirmed. Primary number and, where present, secondary number both validated.	Mail it
D	Confirmed for the primary number only. Secondary (unit or apartment) information was missing.	Mail it, append the unit where you can
S	Confirmed for the primary number only. Secondary information was present but did not validate.	Mail it, correct or drop the bad unit
N	Not confirmed. Primary and, where present, secondary information both failed to validate.	Suppress from the mailing
(blank)	Address was not presented to DPV, usually because it failed to match the ZIP+4 file first.	Investigate before mailing

Alongside that indicator, DPV returns short footnote codes that explain why a record scored the way it did. The ones mailers see most often are:

• AA matched to the ZIP+4 file, and A1 failed to match the ZIP+4 file.
• BB matched to DPV on all components, which is the clean pass.
• CC primary number matched, but the secondary number present did not.
• N1 primary number matched, but the address needs a secondary number that was not supplied.
• M1 primary number missing, and M3 primary number invalid.
• RR or R1 matched to a commercial mail receiving agency.
• U1 matched to a unique ZIP code assigned to a single organization.

Read together, the indicator tells you whether to mail the record and the footnote tells you what to fix. A file full of D and N1 records is a file missing apartment numbers, which SuiteLink and a better source can often repair. A file full of N and A1 records has a deeper data problem. DPV is included in any legitimate CASS pass, so if a vendor cannot show you DPV results, you are not getting a true CASS-certified file.

LACSLink

LACSLink handles addresses converted from rural-route or highway-contract style to standard city-style addresses, usually for 911 emergency-response systems. When a county renumbers a road so emergency services can find homes, the old "RR 2 Box 14" address still sits in databases everywhere. LACSLink matches that legacy format to the new city-style address so the mail still reaches the household, automatically, inside CASS processing.

SuiteLink

SuiteLink improves business addresses by adding missing secondary suite or unit information. Many business records arrive with a correct street address but no suite number, which can stall delivery inside a multi-tenant building. SuiteLink matches the business name and address against USPS data and appends the proper suite where it can. Like LACSLink, it is part of a full CASS pass.

How Software Earns CASS Certification: Cycle O, Stage I, and Stage II

This is the part most guides skip, and it matters if you are buying software or vetting a vendor. USPS certifies address-matching engines on a fixed cycle, and the current designation is Cycle O, which runs through July 31, 2028. Certification is valid until the end of the current biennial period, so vendors must requalify on that schedule to keep producing automation-eligible output.

Two stages are involved, and only one of them is graded.

Stage I is an optional self-test. USPS supplies a file of roughly 150,000 test addresses with the correct answers included, and developers run it, compare their output against the known-good coding, and tune their matching logic. Nothing is graded and nothing is submitted. A vendor can skip it entirely, and most do not, because it is how you arrive at the real test already debugged.

Stage II is the graded examination. USPS supplies a comparable volume of test addresses with no answer key, the vendor processes the file blind and returns the results, and USPS scores it. Passing Stage II is what earns the certification for the cycle.

The passing bar is high, and it is not a single number. To achieve CASS certification, a participant must pass with a minimum score of 98.5 percent 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:

CASS product	Minimum passing score
ZIP+4 coding	98.5 percent
Carrier route coding	98.5 percent
Five-Digit ZIP coding	98.5 percent
LACSLink	98.5 percent
Delivery point coding	100 percent
eLOT	100 percent
DPV or DSF2	100 percent
RDI	100 percent
Perfect Address	100 percent

Reading the table: eLOT (Enhanced Line of Travel) codes the order a carrier walks a route, DSF2 (Delivery Sequence File Second Generation) adds delivery sequence and address-type data, RDI (Residential Delivery Indicator) marks whether a delivery point is residential or business, and Perfect Address removes addresses USPS has no record of ever serving.

Two practical consequences follow. First, if you are licensing software, ask which cycle it is certified for and confirm it is current, because output from a lapsed engine will not support an automation claim. Second, if you are handing the file to a service provider, that requalification burden is theirs, not yours, which is the main reason most mailers never buy postal software at all.

Why CASS Certification Matters

CASS directly affects what you pay in postage, how much of your mail arrives, and how trustworthy your data is over time.

It is required for automation postage discounts. USPS will not grant automation prices on mail that is not CASS-certified and ZIP+4-coded, so skipping CASS means paying non-automation pricing across the whole drop. On any real volume, that gap dwarfs the cost of the CASS pass itself.

Worth stating plainly, because it is commonly overstated: automation is not the cheapest tier in the entire USPS price schedule. High Density Plus and Saturation prices under Enhanced Carrier Route can sit below automation pricing. Those tiers require mailing to nearly every address on a carrier route, which a targeted list by definition does not do. For a list-driven targeted mailing, automation is the tier you are actually competing for, and CASS is the entry ticket to it. For what each class currently costs, see our 2026 USPS postage rates guide.

It cuts undeliverable mail. Every address that fails DPV and slips into your mailing is a piece you paid to print and mail that comes straight back. Filtering those out before the drop is one of the cheapest ways to protect a direct mail budget. For a deeper look at why pieces bounce and how to drive returns down, see our guide to reducing undeliverable mail.

It gives you cleaner data. Standardized, coded addresses are easier to deduplicate, match across systems, and analyze. CASS does not just prepare your file for one mailing; it raises the quality of the database you mail from again and again.

CASS vs NCOA

CASS and NCOA are the two pillars of list hygiene, and they are constantly confused. The simplest way to keep them straight: CASS fixes the address. NCOA fixes the person.

CASS works on the address exactly as written. It standardizes the format, appends ZIP+4, and validates the delivery point. It does not know whether the person who lives there has moved. NCOA (National Change of Address) does the opposite job: it matches your records against the USPS database of people who filed a change-of-address form, then updates the address for movers or flags them when no forwarding address exists.

Dimension	CASS	NCOA
What it fixes	The address (format, ZIP+4, validity)	The person (have they moved?)
Core question	Is this a real, correctly formatted delivery point?	Does this person still live here?
Key components	Standardization, ZIP+4, DPV, LACSLink, SuiteLink	USPS move database match (48 months on Full Service, 18 on Limited)
Postal role	Required for automation discounts	Required for Move Update compliance

You need both. CASS without NCOA delivers a perfectly formatted letter to someone who moved away last year. NCOA without CASS updates the mover but leaves the address in a shape the post office will not discount. Run together, they produce a file that is correctly formatted and currently accurate. For the full breakdown, read what NCOA is and how it works.

How Long a CASS Pass Stays Current

The certification cycle above is the vendor's clock. Yours is shorter and it is the one that governs a drop: a CASS pass is generally treated as current for 180 days from the processing date for automation prices.

The practical rule is simpler than the calendar math. Addresses change constantly, so reprocess your list through CASS before every mailing rather than leaning on an old run. A fresh pass is inexpensive relative to the postage and print it protects, and it guarantees you are coding against the current postal database every time.

How to Get a CASS-Certified List

There are exactly two ways to end up with a CASS-certified file, and one common misconception worth clearing first.

Path 1: Send the list to a CASS-certified mail service provider

This is what most mailers do. You hand the file to a provider that already runs CASS-certified software as part of its workflow, and you get back a standardized, ZIP+4-coded, DPV-validated file plus the PS Form 3553 that documents it. There is no software to license, no cycle to track, and no requalification to manage.

Mail Processing Associates data services processes your addresses through CASS, appends ZIP+4, runs DPV, and applies NCOA in the same pass, then returns a clean, automation-eligible file. Because this runs in-house at our Lakeland, Florida production facility, the cleaned data flows straight into production and presort without a handoff. Our team has been preparing mail this way for 35 years for more than 700 lifetime business customers, and we serve businesses in all 50 states.

Path 2: License CASS-certified software yourself

If you process lists constantly and want the capability in-house, you can license an address-matching engine that holds current CASS certification and run the file yourself. This is the right answer for organizations coding addresses continuously rather than a few times a year, and it is why software vendors sit through Stage II every cycle in the first place.

Two things come with it. You own the license cost and the recertification cadence, and you need the postal data sets the engine depends on kept current. Confirm the product is certified for the current cycle before you rely on its output for an automation claim.

What a free list check does and does not do

Before you choose a path, it helps to know how dirty the data actually is. Our free mailing list health check scans your file in the browser for duplicate records, missing or malformed fields, and bad ZIP codes, and estimates the postage you are about to waste. It will tell you whether you are looking at a routine CASS pass or a file that needs heavier cleanup first.

To be plain about the limit: the health check does not produce a CASS-certified file. It is a diagnostic. Certification only comes from running the data through CASS-certified software, by one of the two paths above. Use the health check to size the problem, then pick the path.

CASS is also the front end of the broader mailing workflow. Once your list is certified and coded, the next step is sorting and barcoding it to earn the discount, which is where presort mail services come in. To have the whole sequence handled together, our mailing services bundle CASS, NCOA, presort, and the USPS handoff into one managed job.

The Takeaway

CASS certification turns raw addresses into postal-grade data: it standardizes every address to Publication 28, appends ZIP+4, validates deliverability through DPV, and applies LACSLink and SuiteLink. That clean file is what makes a targeted mailing eligible for automation pricing and keeps undeliverable pieces out of your drop. Pair it with NCOA, reprocess before every mailing, and the address half of your direct mail program is solved.

Frequently Asked Questions

What does CASS certified mean?

CASS certified means a mailing list was processed through USPS-certified address-matching software. Every address is standardized to USPS format, given a ZIP+4 code, and checked against Delivery Point Validation (DPV) to confirm it is a real, deliverable address. A CASS-certified list is the baseline USPS requires before it will grant automation postage discounts.

Is CASS the same as NCOA?

No. CASS standardizes and validates the address as it is written, correcting format, adding ZIP+4, and confirming the delivery point exists. NCOA updates the person, matching your records against USPS move filings so mail follows people who relocated. A clean list needs both: CASS fixes the address, NCOA catches the movers. They run together but solve different problems.

How long is CASS certification good for?

Two clocks apply. The software carries CASS certification for a cycle, currently Cycle O running through July 31, 2028, and vendors requalify on that schedule. Your processed list is a separate matter: a CASS pass is generally treated as current for 180 days from the processing date for automation pricing, and because addresses change continuously, best practice is to reprocess before every mailing.

What do the DPV codes Y, D, S, and N mean?

They are the Delivery Point Validation confirmation indicators on each record. Y means the address was confirmed including any secondary unit number. D means the primary number confirmed but secondary information was missing. S means the primary number confirmed but the secondary information supplied did not validate. N means the address failed to confirm and should be suppressed from the mailing.

Do I need a CASS-certified list for bulk mail?

Yes, if you want automation postage discounts. USPS requires CASS-certified, ZIP+4-coded addresses to qualify commercial mail for automation rates on First-Class Mail and USPS Marketing Mail. Without CASS the post office charges higher non-automation pricing, and undeliverable pieces waste print and postage. For any bulk drop, CASS is a required step.

What is DPV?

DPV stands for Delivery Point Validation. It is the USPS data set, applied during a CASS pass, that confirms whether an address is an actual deliverable delivery point, not just a correctly formatted one. CASS checks the format; DPV checks that the address physically exists and receives mail. A record can pass CASS formatting yet fail DPV if the building number was never built, which is why DPV is the part that keeps undeliverable pieces out of your mailing.