Making Smarter Decisions: How to Connect CASS™, NCOALink®, and ACS™

By Adam Collinson

Address Quality Series · Article 6 of 8 · [See all articles →]

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A mailer once asked, “We’re running CASS™, processing through NCOA^Link®, and using ACS™. Our deliverability still isn’t where we want it. What are we doing wrong?”

The problem wasn’t the tools.

The problem was that they were treating each tool as a standalone process rather than as connected components of an integrated system. They had the ingredients but weren’t following a recipe.

Address quality best practices isn’t about running each process in isolation. It’s about connecting the dots between CASS™, NCOA^Link®, and ACS™ data (all of the data) to make smarter decisions at every stage. Let me show you how.

The Framework for Smart Decision-Making

Think of address quality data in layers. Each layer provides different information, and the magic happens when you stack them together:

1. CASS™ standardizes an address and tells you if an address is valid according to USPS databases. It confirms the address exists in their systems and assigns codes indicating characteristics and potential issues.
2. NCOA^Link® tells you if someone moved. It provides move information before you mail, allowing you to update addresses proactively.  But, it has restrictions in making matches and returning new addresses.
3. ACS™ tells you what actually happened when you mailed a piece. It provides real-world feedback from USPS equipment and carriers who attempted to deliver your mail.

Each provides vital information, and allows for some decision-making.  But combined strategically, they enable more and better decision-making that significantly improves deliverability while reducing waste and risks.

Decision Point One: Is This CASS™ Error Critical?

CASS™ will flag addresses with errors or deficiencies. The question is: which ones actually matter, and what should you do next?

Consider an address that fails DPV^® validation with an invalid primary number. Is this critical? It depends.

First, check your ACS™ history. If you have a prior ACS™ return showing “No Such Number” for this address, then yes, it’s critical. The address doesn’t exist, and you’ve got confirmation from a carrier who tried to deliver the piece but couldn’t determine the correct location. Suppress this address or investigate further before mailing again.

If you have no prior ACS™ returns for this address, the situation is different. It could be new construction that hasn’t yet been added to the USPS database. In that case, consider mailing it with ACS™ to gather information. If the address starts to CASS™‑validate within a few months, it was likely new construction. If it still doesn’t validate and ACS™ returns show nondelivery, flag it for corrective action at the top of your worklist.

Now consider an address that’s missing secondary information (CASS™ shows DPV^® D with footnote N1) or where the secondary information is not valid but needed (CASS™ shows DPV^® S with footnote C1). The real question is: does the carrier actually need that secondary information to deliver?

If you have mailed to that address before and there are no prior ACS™ returns for it, the carrier has been able to determine delivery without the validated unit number. The missing information isn’t critical yet. Keep mailing, but put the record on a lower‑priority worklist to be corrected over time.

If you have a prior ACS™ return showing “Insufficient Address” for that address, that confirms the carrier does need the secondary information. Raise the priority of this record. Go back to your source and obtain the complete address before mailing again. If that’s not possible, consider other services or data sources that can supply the missing unit information.

Also remember: missing or incorrect secondary data can block matches to Change of Address records, and a new carrier may not have the local knowledge to figure out delivery.

This is how you connect CASS™ and ACS™ data to make smarter, risk‑aware mailing decisions instead of treating every CASS™ error the same.

Decision Point Two: Is This Vacant Address Really Vacant?

CASS™ identifies some addresses flagged by carriers as vacant for at least 90 days. But this vacant indicator is address-based, not person-based. What if someone just moved in?

This is where combining CASS™, NCOA^Link®, and ACS™ data becomes powerful: 

• CASS™ vacancy is address-based.
• NCOA^Link® and ACS™ are name and address-based.

Here are the steps:

Step 1: Check NCOA^Link®. Do the NCOA^Link® results indicate that the person moved from that address?

Step 2: Check ACS™ history for that specific person at that address. Does it indicate they moved, either because of a COA-related result or a Vacant record?  If there’s an ACS™ vacant, it means that the contact used to be there and the address went vacant after they moved out. This confirms the vacant status is relevant to your target.

If there’s no ACS™ return for that person at that address, the situation is different. The person might have just moved in, and the carrier’s updated vacant status is still being processed (will take weeks to a month or two). Consider mailing with an ACS™ endorsement to verify.

This same logic applies to other CASS™ characteristics that indicate a probability of delivery issues. ACS™ results can be used to increase or decrease that probability. Remember, CASS™ provides a snapshot based on the current USPS databases, while ACS™ provides actual delivery history for both the address and your specific targets.

Used together, CASS™, NCOA^Link®, and ACS™ let you treat “Vacant” as a signal to investigate, not an automatic reason to give up on that address.

Decision Point Three: When Perfect Addresses Still Fail

Here’s a scenario that surprises many people: 100% of addresses in a ZIP Code fail CASS™, yet they’re all deliverable. 

How is this possible?

Some Military ZIP Codes not using the standard USPS military addressing format will fail CASS™ validation. But the USPS delivers to the military post, and the military post can determine correct delivery. The addresses work even though they don’t validate.

There are several other scenarios where the majority of addresses fail CASS™ validation, and do not qualify for postage discount, yet the vast majority still get delivered.

For all of these, check prior ACS™ returns. Are you actually getting delivery confirmations? Or are you getting returns indicating problems? ACS™ tells you what’s really happening on the ground, regardless of what CASS™ validation suggests. And when you see a pattern or a higher rate of ACS™ returns for addresses in a certain location or with certain address characteristics, investigate. 

For example, pieces to a particular ZIP are getting ACS™ returns at a high rate and with the same reason codes: 

• Possibility 1 (And yes, I have seen this multiple times): Pieces are getting mailed to what are supposed to be invalid, internal test addresses. In one case, they used a ZIP of ‘12345’. The problem is that it’s a valid ZIP Code with valid addresses. The addresses for the test accounts/records need to be updated to not use a valid ZIP.
• Possibility 2: There are over 1 million R777 and R779 street addresses. These are valid, physical locations in areas where the USPS does not deliver to. Instead, the residents receive their mail via a PO BOX. So, mail to the street address requires effort by postal clerks to try to determine and route mail to the correct PO Box. While DPV^® shows Y (valid), these addresses are about 20 times more likely to be undeliverable than standard addresses.  

How do you know if delivery is a problem for your specific R777/9 addresses? Check prior ACS™ returns. If you’ve got confirmation of non-deliverability through ACS™, that validates the concern. If you haven’t had issues, the address might be working despite the characteristic – at least for now.

NOTE: These addresses started losing discounts with CASS™ Cycle O, and the USPS stopped accepting COAs to or from these addresses a few years ago. But the decision about whether to mail to them depends on your actual experience, which ACS™ documents. And, at least you know the corrective action: contact the recipient and ask for their PO BOX mailing address.  

FYI, If you want to maintain contact with these recipients, you really want to get their PO BOX mailing address, as the USPS will not allow Changes of Address from the street address, only from the PO BOX address.

Decision Point Four: Time of Mailing Strategies

Prior ACS™ data informs strategies at the time of mailing, especially in two situations: when there’s an issue with the person at a good address, and when NCOA^Link® provides only a near or partial match.

Suppose prior ACS™ returns indicate an issue with the person at an address (like ANK, Attempted Not Known). What does this tell you? The address itself is good. The USPS can deliver there. But the person you’re trying to reach isn’t at that location. 

This creates an opportunity. Consider using alternative addressing (like “Or Current Resident”) to ensure deliverability to whoever currently lives at that address. You might not reach your original target, but you can still reach someone at a valid, known‑good address.

Nos suppose NCOA^Link® provided a near match or partial match, and couldn’t provide a new address with confidence. How do you handle this?

First, look at historical ACS™ results. Do they give you a new address to use, or supporting non‑delivery information for that person?

• If this is a marketing piece, consider using alternative addressing (“Or Current Resident”) so you still reach someone at that location.
• If you need to maintain contact with that specific recipient, mail to the old address with an ACS™ endorsement and let carriers break the tie. If the person has actually moved, you’ll get an ACS™ return with the new address. If they haven’t moved, the piece gets delivered.

This approach leverages local carrier knowledge that neither CASS™ nor NCOA^Link® possesses.

Also factor in the Move Effective Date and the address type before making this decision. If the NCOA^Link® match showed an older move that NCOA^Link® flagged but couldn’t resolve, it may be past the forwarding time or even outside the ACS™ data window the USPS uses.

The key is using multiple data sources to choose a well‑informed strategy at the time of mailing, rather than applying a one‑size‑fits‑all rule.

Decision Point Five: Guiding Corrective Actions

Different ACS™ reason codes should trigger different corrective actions, especially when combined with other data sources and based on your specific business and mailing needs.

For COA, MLNA, and BCNO returns, the corrective action is clear: have an agent contact the person to confirm or obtain the new address. But go deeper than that.

For MLNA and BCNO situations specifically, rerun NCOA^Link® in the future. Sometimes people file a COA a few weeks or months after they actually moved. Your future NCOA^Link® processing might capture what the initial processing missed.

For Insufficient Address returns, use them in combination with CASS™ results to target your data collection efforts. The ACS™ return confirms you need specific information. The CASS™ codes tell you what type of information (primary versus secondary).  If the issue is with the Primary number, there is no point sending this record to an Apartment Append type of service.  Using this information allows you to look for or ask for specific corrections rather than requesting a complete address re-validation.

This targeted approach is always more efficient than blanket data cleanup efforts.

Decision Point Six: Pattern Recognition

Individual decisions matter, and patterns matter even more. This is where trending and analysis become critical.

Are certain list sources consistently generating higher ACS™ return rates? That should inform future purchasing decisions.

Are certain CASS™ characteristics correlating with higher undeliverable rates? That should inform mailing strategies. Maybe addresses with certain footnote codes should be handled differently, or maybe they should be suppressed entirely.

Are addresses with certain status and characteristics resulting in lower or higher response rates? Use those response patterns to better select addresses for future campaigns.

Is there a pattern that points back to an issue in one of your processes? Here is one of my favorites. 

I was looking at CASS™ failures due to invalid street names. These are often simple typos, relatively easy to fix. For one client, I noticed a pattern of CASS™‑failing addresses that were not resulting in ACS™ records, and I tied them back to a client using AI voice recognition to capture address information.  

That sounds fine in theory, but addresses have their own language. Say “10 1/2 MAIN ST” out loud. That’s a CASS™‑standardized street address. But the voice recognition software at the time interpreted it as “10 AND A HALF MAIN STREET.” Pass that into CASS™ and it does not recognize “AND A HALF MAIN” as a valid street name—no automation discounts. Yet mail with this address gets delivered, because it’s pretty easy for the carrier to figure out.  

I identified a couple dozen related patterns. After correcting these issues, about 96% of those addresses CASS™‑validated. And remember, addresses that do not CASS™‑validate cannot be matched to COAs by NCOA^Link®. Once corrected, 8% of those addresses matched to a COA.

The only way to identify some of these patterns is by analyzing CASS™, NCOA^Link®, and ACS™ data together over time, not in isolation.

The Risk Management Application

Combining data sources enables higher confidence and more sophisticated risk management strategies, particularly for fraud prevention and PII protection.

Flag at-risk addresses using CASS™ characteristics (like CMRA without PMB designation, or recent DPV^® validation failures). Then layer on NCOA^Link® data (factor in the Move Effective Date and if a new address is available). Then add ACS™ historical information (prior returns suggest delivery issues).

For addresses that score high on multiple risk factors, use appropriate, alternative processes. Instead of mailing sensitive documents directly, mail a postcard with ACS™ at low cost and low risk. The postcard contains no PII, allowing the USPS to dispose of it if undeliverable.

Based on whether you receive an ACS™ return, you make different decisions about the full mailing. This approach manages risk while maintaining customer service quality and can even result in an overall cost savings.

Performance Measuring That Drives Improvement

The combination of CASS™, NCOA^Link®, and ACS™ data enables performance measurement that actually drives improvement.

Measure deliverability rates by list provider or source. Which vendors consistently provide the best addresses? Use that information in future contracts and negotiations.

Measure deliverability rates by address quality level or indicator. Recent COAs not applied might show 90% undeliverable rates on Marketing Mail, but response rates might still be high enough to justify mailing. That’s a business decision informed by data, not a reflexive suppression.

Measure deliverability rates by address characteristics. In a mailing targeting small to medium businesses, using Alternative Addressing on NoStats Drop addresses might show 40% undeliverable rates, higher still if secondary information is missing. But in some business contexts, that’s acceptable.

Small business mailings are a perfect example. The deliverability challenges are known and documented. But if the response rates justify the waste, you mail anyway. The key is knowing the numbers and making informed decisions, not assuming every undeliverable piece is a failure.

Don’t forget to use ACSTM on these marketing mailings.  Identify which addresses result in undeliverable mail and do not keep sending pieces over and over again.

The Reports That Matter

Three key reports provide the data you need for this integrated approach:

1. The CASS™ 3553 report includes a standardized high-level section and a detailed customized section that varies by CASS™ engine. Don’t ignore the detailed section. That’s where the actionable intelligence lives.
2. The NCOA^Link® Processing Summary Report includes standardized high-level statistics and detailed customized information about matches, CASS™ results, DPV^® validation, and more.
3. The NCOA^Link® Customer Service Log provides one row per run with statistics on CASS™, DPV^®, LACS^Link®, Suite^Link®, and NCOA^Link® performance. Manage ListIDs carefully to enable trending and comparison over time.  

NOTE: this is not a standard report returned to NCOA^Link® users. This is a report sent to the USPS by the NCOA^Link® Licensees on a monthly basis. So, ask your NCOA^Link® vendor if they offer this data in some manner or analysis based on this data.

If you have multiple lists and databases, this data allows you to also compare how they are performing against one another.  If different sources should be the same, but are not, what is different with the processes around those sources? Is something broken in one? Or is one making use of an additional tool/process that the others could also use?

These reports are only valuable if you actually use them to drive decisions and track performance over time.

Data without analysis is noise.

The Tools Are Necessary But Not Sufficient

Here’s the reality that many organizations miss: having access to CASS™, NCOA^Link®, and ACS™ isn’t enough. Running the processes isn’t enough. You need expertise to fully interpret the results and make smart decisions.

This is why working with experienced partners matters. 

At GrayHair Software, we don’t just run addresses through processing engines and return results. We analyze CASS™ codes in context. We evaluate NCOA^Link® matches considering business objectives. We interpret ACS™ returns in light of the complete picture. We provide specific recommendations for different categories of addresses.

That’s the difference between compliance-based mailing and intelligence-driven mailing.

The Integration Challenge

The biggest obstacle most organizations face isn’t access to tools or data. It’s integration.

CASS™ processing might happen in the mail shop. 

NCOA^Link® updates might be handled by marketing operations. 

ACS™ data might be captured by customer service. 

If these groups don’t talk to each other and share data, the organization never benefits from the complete picture.

Breaking down these silos requires both technology (systems that share data across functions) and process (workflows that ensure the right people see the right information at the right time).

It also requires a shift in thinking. Address quality isn’t just a mailing issue. It’s not just a marketing issue. It’s not just a billing, shipping, or service issue.  It’s a business issue that touches many operations, sales, marketing, customer service, fraud prevention, regulatory compliance, and operational efficiency.

Starting Small and Scaling Up

If this all sounds overwhelming, start small. Pick one decision point and improve it.

Maybe start with CASS™ errors. Instead of automatically mailing every address that passes basic validation, check ACS™ history for addresses with known issues. Suppress or investigate before mailing.

Or start with NCOA^Link® near matches. Make sure to mail them with ACS™ endorsement to gather information.

As you gain confidence and demonstrate results, expand to additional decision points. Build the infrastructure and processes over time. Create feedback loops that capture learnings and apply them systematically.

The Competitive Advantage

Here’s what I’ve observed over 25 years in the postal industry: most organizations run CASS™  and NCOA^Link® because it is the easiest way to qualify for postage discounts. They may participate in ACS™ because they should and/or to get additional COAs. But very few organizations truly connect these data sources to make the smartest decision possible.

That gap represents opportunity. The mailers achieving best-in-class results aren’t using different tools than everyone else. They’re using the same tools more intelligently.

They understand that nothing is 100%. They recognize that different address situations require different strategies. They leverage actual delivery experience to inform future decisions. They measure performance and continuously improve.

That’s how you transform address quality from a compliance checkbox into a competitive advantage.

In the next article, we’ll explore best practices across the entire address quality lifecycle, from initial data entry through database maintenance to just-in-time processing and return mail handling. Because connecting the dots at decision points matters, but so does building a comprehensive system that maintains quality over time.

For now, remember: the tools provide data, but you provide the intelligence. The difference between good results and great results is in how you connect those dots.

Next in this series

• Address Quality Best Practices: From Entry to Delivery
• The #1 Rule in Address Quality: Nothing is 100% (And Why That’s OK)

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