CASS™ Certification Explained: What Those Codes Really Mean

By Adam Collinson

Address Quality Series · Article 3 of 8 · [See all articles →]

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Every year, I meet mailers who proudly announce they’re “CASS™ certified” as if it’s a badge of honor. 

I hate to break it to them, but that’s not how it works. CASS™ doesn’t certify mailers. It certifies the software that processes addresses.

That misunderstanding matters. If you don’t grasp what CASS™ really does, you’re almost certainly leaving intelligence and money on the table.

Let’s clear it up. In this article, I’ll explain what CASS™ actually does, why it matters, and most importantly, what all those cryptic codes in your CASS™ reports are trying to tell you. Because those codes aren’t just technical noise. They’re decision-making tools.

What CASS™ Actually Is

CASS™  stands for Coding Accuracy Support System. It’s a USPS certification program for address-matching software. When software is CASS™ certified, it means the USPS has tested and approved that software’s ability to:

• Standardize addresses.
• Assign correct ZIP codes and ZIP+4 codes.
• Assign carrier route codes.
• Validate delivery points and identify whether an address is actually deliverable.

Here’s the critical part: running your mail through CASS™-certified software is mandatory for qualifying for USPS automation and presort discounts. Not optional. Not recommended. Required.

But CASS™ does far more than just qualify you for discounts. It standardizes the address to enable additional processing to validate addresses, identify issues, provide detailed information about address characteristics, identify needed changes, identify enhancements, enable the ability to look for Changes of Address, and give you the data you need to make informed decisions about which pieces to mail and which to suppress.

CASS™ doesn’t just clean addresses. It creates structured intelligence.

The CASS™ Processing Cycle

When you submit addresses for CASS™ processing, the software standardizes the format, validates components, and matches the address against USPS databases. This happens through several integrated processes, in a very specific order:

1. First, the address is standardized to conform to USPS formatting rules. Abbreviations get applied consistently. Elements get positioned in the right order. Extraneous information gets identified.
2. Next, the address gets matched against the USPS ZIP+4 database. This confirms the address exists in their systems and assigns the correct codes.
3. Then comes DPV^® (Delivery Point Validation), which confirms whether that specific address is actually deliverable. An address can be in the ZIP+4 database but still not be a valid delivery point.
4. Additional processes, such as LACS^Link® (for rural route conversions), Suite^Link® (for secondary address information), and RDI™ (Residential Delivery Indicator), enhance the data with more specific information.
5. Finally, you get a result code, footnote codes, and various other indicators that tell you exactly what the software found, what it fixed, and what issues remain.

Understanding DPV^® Result Codes

DPV^® is where things get interesting. With the latest CASS™ requirements, there are both DPV^® and Enhanced DPV^® fields. Many organizations have not yet transitioned fully to Enhanced DPV^®. The result code tells you whether the address is confirmed, and the footnote codes tell you the details:

• A DPV^® result of Y means the address is confirmed as a valid delivery point. Great news. You’ve got a good address, at least from a structure standpoint.  But not all ‘Y’ addresses are valid for mail delivery.  You need to inspect other results to make that determination.
• A DPV^® result of S means the address contained secondary address information that the USPS’s data could not confirm.  The challenge is that there are multiple potential causes.  1) The USPS has secondary data and it does not match.  2) The secondary data is more like internal mail stop information, so the USPS data does not have secondary address data for this address because the USPS does not need it for delivery.  This is where you need to make a business decision, and more data would help – if not needed, good to go.  But, if needed, need to ask / confirm the secondary information 
• A DPV^® result of D means the address is confirmed but missing secondary information (like an apartment number). This is where you need to make a business decision. Is the missing secondary information critical for delivery, or can the carrier figure it out?
• A DPV^® result of N means the address is not confirmed but falls within a known range of addresses. This could mean several things, and that’s where the footnote codes become essential.
• A DPV^® result of blank means the address could not even be evaluated.  The CASSTM error codes need to be evaluated to determine the level of the issue, from just outside of the known range of address on a street, to street name not recognized, to missing critical address information, to it looks like a foreign address.

With the Enhanced DPV^® codes, addresses where the secondary is present but not needed (and so not validated) by the USPS are Y’s. Additionally, valid addresses that the USPS does not deliver to are assigned a result of ‘R’ instead of Y- but not 100% of the time.  Other CASS™ results should be checked to ensure identification of all such addresses.

Decoding DPV^® Footnote Codes

Here’s where most people’s eyes glaze over, but stay with me because this is where the real value lives.

The DPV^® Footnote codes are a string of values that apply to a given address; they tell you exactly what happened.  

Core Validation Codes

• Footnote AA means the address matched to the ZIP+4 file. Combined with a DPV^® result of Y, you’ve got a confirmed, valid address.  But, you need to evaluate other Footnote Codes to determine deliverability.
• Footnote A1 indicates the address didn’t match to the ZIP+4 file. If you see this with DPV^® result N, you’ve got a problem. The USPS doesn’t recognize this address in their database.
• Footnote BB means the entire address matched, including secondary information. This is your first target, an address with a BB footnote.
• Footnote CC means the street address matched, and there was secondary information present that the USPS could not validate because the USPS does not need secondary data to deliver the piece. For example, the address is a retirement community where the USPS delivers all the mail to a front office. But the residents all have their own Unit Number, which the office uses to sort and deliver the mail internally to the correct recipient.

Secondary Issues

• Footnote C1 means the street address matched, the address requires secondary address data, there was secondary information present, but it does not match what the USPS has for valid secondary data for that address.  
• Footnote N1 means the street address matched, the address requires secondary address data, but there was no secondary information present in the address.  

Primary Number Issues

• Footnote M1 indicates a primary number is missing. This is a serious issue. Without a house number, delivery is much less likely.
• Footnote M3 means the primary number is out of range for that street. The address might look right, but it doesn’t exist according to USPS data. The impact on deliverability will depend on the nature of why it is out of range.  That often requires evaluation of the address itself.  Often, this leads to the identification of a recurring address entry error impacting many addresses.  

Good news, mailers can often work to change the address entry processes to prevent this in the future.  And in many cases, there are ways to bulk-identify and fix addresses with the same type of issue.

Rural Route Issues

• Footnote P1 means the address is missing a PO BOX, Rural Route (RR), or Highway Contract (HC) number. This BOX number is the primary number for these types of addresses (so, similar to the M1 Footnote for other addresses).
• Footnote P3 means the address is a PO BOX, Rural Route (RR), or Highway Contract (HC) but that the BOX number is not valid (so, similar to the M1 Footnote for other addresses). 
• Footnotes RR and R1 indicate that the address is a CMRA (Commercial Mail Receiving Agency).  The USPS delivers to the address for this agency, which then delivers to the recipient’s rented box. These are identified via Private MailBox (PMB) numbers assigned by the CMRA. RR indicates that a PMB was detected in the address, while R1 indicates that a PMB was not detected in the address.

NOTE: The USPS does not allow individuals and families renting a box with a CMRA to file a COA from the CMRA.  The CMRA’s are required to provide limited forwarding services.  So, on CMRA and some other types of addresses, you may want to maintain their prior address as well, obtain a separate physical address, or obtain an alternate means of contacting them (email, phone…)

Special Situations

• Footnote R7 means the address is a street-style address that has been validated as a residential or business address in an area where the USPS does not deliver to those addresses. Mail delivery is via a PO BOX.
• Footnote TA means the input address had a single trailing alpha on the primary number, and the address could be validated by treating that trailing alpha as secondary address information. 

For example, home at 123 MAIN ST turn the basement of ara above the garage, or back building into an apartment and they decide to identify it as 123B MAIN ST. The primary number of 123B is not in the USPS’s data (so, not valid).  But, in treating the address like “123 MAIN ST #B”, CASS™ was at least able to validate the primary address information.

• Footnote PB indicates the address is a PBSA (PO BOX Street Address equivalent). Meaning, delivery is actually to a PO BOX at the Post Office represented by the primary address information.
• Footnote IA indicates an Informed Address. This is still under development at this time, and should not be encountered.

Special Address Characteristics

Beyond basic validation, CASS™ identifies special characteristics that affect how you should handle addresses.

NoStat addresses are locations where the USPS does not perform final delivery for a variety of reasons. The NoStat Reason code can be evaluated to determine the actual reason; they include:

• No Structure / New Construction / a vacant Rural Route address, to which mail delivery is not currently established.
• Drop addresses indicate mail goes to a central location rather than individual units. These are common at universities, military bases, highrises, gated communities, and large businesses.
• R777/9 addresses indicate the address is in an area where the USPS does not deliver to the physical addresses.

Throwback addresses are where the USPS would deliver to the address, but the current occupant has requested that all mail to that address be re-directed to and delivered via PO BOX address.

GoPost addresses are USPS parcel locker locations. These are valid for package delivery ONLY. Other mail to these addresses will be processed as Undeliverable As Addresses (UAA).

Vacant addresses have been confirmed by carriers as unoccupied for at least 90 days. This is a significant red flag, especially if you’re trying to reach a specific person.  

NOTE: Rural Route addresses do not get flagged as Vacant. Instead, they are coded as a NoStat address.

The Reality of “Bad” Addresses

Here’s something that surprises many people: just because an address fails CASS™ doesn’t mean it’s undeliverable.

New construction addresses fail CASS™ regularly because they’re not yet in the USPS database. But they’re perfectly deliverable. The carrier knows the new house exists even if the database hasn’t caught up.

Some valid physical addresses don’t follow standard formatting rules. Military addresses often fail CASS™ if they’re not using the proper military addressing format, but they still get delivered because the military post office can figure it out.

Many simple issues can prevent CASS™ coding, but carriers and clerks can easily figure out the correct delivery location. For example, a carrier can easily figure out that CASS™ failing addresses like “100 HALF MAIN ST,” “1OO 1/2 MAIN ST,” or “100 1/2 MIAN ST” should get delivered to “100 1/2 MAIN ST,” especially if they also recognize the name on the piece.

Conversely, some addresses pass CASS™ with flying colors but still aren’t deliverable. An address can be structurally perfect and in all the right databases but still be wrong for the person you’re trying to reach.

This is why CASS™ is necessary but not sufficient on its own for achieving high deliverability rates.

The CASS™ 3553 Report

After processing, you receive a CASS™ 3553 report. This report has two sections, and both matter:

1. The first section is standardized and high-level. It serves as proof that you performed CASS processing to qualify for postage discounts.  It shows overall match rates, validation percentages, and summary statistics. This is useful for quick assessment and trend comparison.
2. The second section is detailed and customized by each CASS™ engine vendor. This is where you find more specifics about what happened to each address, what codes were assigned, and what issues were identified.

Ignore the second section at your peril. That’s where the actionable intelligence lives.

Making Decisions with CASS™ Data

CASS™ data should drive specific actions. Not all addresses deserve the same treatment.

Addresses with DPV^® blank and footnote M3 (primary number out of range) are questionable – but potentially easily fixable. Unless you have additional information suggesting the address is valid, these should be flagged for review and potentially suppressed.

Addresses with DPV^® D and footnote N1 (missing secondary information) require context. Check your ACS™ data from prior mailings. If you’ve successfully delivered to this address before, it means the carrier has a way to potentially determine the missing secondary information and complete delivery.  But, you should not rely on that being the case 100% of the time.  If you’ve received an ACS™ return indicating “Insufficient Address,” you should obtain the unit number before mailing again.

Addresses flagged as vacant require careful consideration. For example, if you’re mailing to a specific person, check NCOA^Link® to see if they’ve filed a change of address. If they haven’t, consider suppressing the piece or using an alternative verification method – UNLESS you have a reason to believe that they just moved into that address..

Industry-Specific Considerations

Different industries have different requirements for address validation:

• Financial institutions dealing with the Bank Secrecy Act need a physical address. PO BOX, PBSA, CMRA, and other addresses do not meet this regulatory requirement for customer identification programs.
• Healthcare organizations with HIPAA concerns need to ensure mail reaches the right person at the right location. Deficient or outdated addresses introduce risks of mis-deliveries..
• Government agencies often have restrictions on certain address types. Understanding CASS™ codes helps ensure compliance.

Beyond Postage Discounts

Remember, CASS™ is mandatory for postage discounts, but its value to businesses extends far beyond qualifying for lower rates.

CASS™ data helps you identify fraud risks. Unusual address patterns, high-risk characteristics, and validation failures can all signal potential fraud.

CASS™ results inform customer service strategies. If you know an address has issues, you can proactively reach out to confirm information rather than waiting for returned mail. Addresses with deficiencies or certain characteristics that may even still qualify for Postage Discounts have undeliverable rates 10x, 20x, or even 30x higher than addresses without deficiencies or special characteristics.

CASS™ codes combined with other data sources like NCOA^Link® and ACS™ enable sophisticated decision-making about which pieces to mail, which to suppress, and which require additional verification.

Working with Service Providers

Most mailers don’t run CASS™ software themselves. They work with mail service providers or specialized address quality companies.

When evaluating providers, ask about more than just CASS™ certification:

• How they use CASS™ data to inform recommendations.
• What level of detail they provide in reporting.
• How they combine CASS™ results with other data sources like NCOA^Link® and ACS™.

At GrayHair Software, we don’t just run addresses through CASS™ and hand back results. We analyze the CASS™ codes in context, combine them with NCOA^Link® and ACS™ data, and provide specific recommendations for each category of addresses.

That’s the difference between basic compliance and actual address quality management.

The Timing Question

Just because you have a good, CASSTM certified address does not mean you are done.  Because address data changes constantly.  That is why the requirement for discounts is that you run CASSTM on all addresses within a certain time period prior to the mailing.

Besides the addition of Suite^Link® and LACS^Link® records, regular address information changes all the time due to the introduction of new construction, the destruction of other addresses, and the USPS ongoing efforts to maintain efficient routes based on changing mail volumes.  In fact, in a month, here are the typical changes that occur in the USPS’s data:

• 100,067 Delivery Points added.
• 40,387 ZIP+4’s added.
• 72,426 Addresses moved to a different ZIP+4.
• 6,654 Changes to preferred Last Line data (City, State, ZIP).
• 419,339 Addresses moved to different carrier routes.
• 17,996,752 Addresses with delivery sequence changes.

The Bottom Line

CASS™ certification is mandatory for postage discounts, but that’s the least interesting thing about it. The real value lies in understanding what those result codes and footnote codes are telling you about your addresses.

Every code represents an opportunity to make a better decision. Every footnote is a data point that can inform your strategy. Every validation result is a chance to improve your deliverability and reduce waste.

In the next article, we’ll explore NCOA^Link® and how move update processing fits into the broader picture of address quality. Because CASS™ tells you if an address is structurally valid, but NCOA^Link® tells you if the person is still there. Both matter, and neither is sufficient on its own.

For now, the next time you look at a CASS™ report, don’t just check the overall match rate. Dig into those footnote codes. That’s where the intelligence lives, and that’s where the opportunities hide.

Next in this series

• NCOA^Link®: Beyond the Basics of Move Updates
• ACS™ Data: The Missing Link in Your Address Quality Strategy
• Making Smarter Decisions: How to Connect CASS™, NCOA^Link®, and ACS™

Want to go deeper on address quality? Visit our Address Quality hub for tools, strategies, and real-world best practices.