ACS™ Data: The Missing Link in Your Address Quality Strategy

By Adam Collinson

Address Quality Series · Article 5 of 8 · [See all articles →]

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Here’s a scenario I see more often than not: A mailer runs CASS™, processes through NCOA^Link®, qualifies for all the postage discounts, and still experiences undeliverable rates of 5% or higher. 

They’re frustrated because they followed all the rules, checked all the boxes, and the mail still isn’t getting delivered.  When I ask what they do with the returned, undeliverable mail, it’s piled up somewhere.  They look at some of it when they can, and just dispose of the oldest pieces when the pile gets too big.  And I start to bang my head.

The conversation usually goes like this:

“Are you using ACS™?”

“ACS™? Isn’t that just another way to meet the Move Update requirement, but only with some mail? We use NCOA^Link® because we need to meet the requirement on all our mailings.”

That question reveals the fundamental misunderstandings that cost mailers millions of dollars annually. ACS™ is not just about the Move Update requirement, and NCOA^Link® vs ACS™ is not an either/or. It’s about complementing NCOA^Link® and closing the loop on address quality. 

It’s the missing link that transforms compliance-based mailing into intelligence-driven mailing and business operations.

What ACS™ Actually Is

ACS™ stands for Address Change Service. It’s a program that provides mailers with information about what happened to their mail after it entered the postal system. Specifically, it tells you which pieces were undeliverable and why.

When you participate in ACS™, the USPS returns information about undeliverable mailpieces in an electronic format ready for processing.  The exact method depends on whether you’re using Traditional ACS™, OneCode ACS^®, or Full-Service ACS™, and whether you have elected SingleSource data fulfillment.

The critical point is this: ACS™ gives you actual, real-world feedback from the USPS system, carriers, and clerks who attempted to process and deliver your mail. 

This information is gold.

ACS™ is also an approved method to meet the USPS’s Move Update requirement. However, there is a very important “but”: The Move Update requirement calls for checking and applying Change of Address updates within 85 days prior to the actual mailing. ACS™ provides information after the mailing. So, using ACS™ on a mail piece does not qualify that piece for meeting the Move Update requirement. It qualifies any subsequent mail pieces mailed in the next 95 days (updated with any new address information that gets provided).

Why ACS™ Data Matters

Let’s break it down:

• CASS™ tells you if an address is structurally valid according to USPS databases. It also returns information and flags that indicate different levels of potential issues with delivery. 
• NCOA^Link® tells you if someone filed a change-of-address and, hopefully, provides the new address. But not always. 

Neither tells you what actually happened when delivery was actually attempted to that name and address.

That’s what ACS™ provides. It’s the difference between theoretical deliverability and actual delivery results.

Did the carrier return the piece because the person moved? That’s valuable information you can act on. Did they return it because the person is not known at that address? That’s different from a move and requires a different response. Did they return it because the address is unknown or insufficient?  That calls for a whole different set of actions.  Did they return it because the person is deceased? That’s critical information with both business and compliance implications.

ACS™ closes the loop. It transforms your mailing list from a static database into a living system that learns and improves with each campaign.

The Types of ACS™ Returns

ACS™ returns are classified by reason codes. Understanding these codes is essential for taking appropriate action. Rather than walking through each one in long paragraphs, it helps to see them side by side.

Below is a summary of the key ACS™ reason codes, followed by short notes where the nuances really matter.

Summary Table: Core ACS™ Reason Codes

Code / Term	What it means	What it tells you	Typical action
COA with new address	A change-of-address was filed and a new address is available. ACS™ also provides how the COA was filed (Individual, Family, Business), the Move Effective Date, and the Made Available Date.	The person, family, or business is no longer at the old address, and USPS has a new one. You also know when the move was effective and when USPS made it available.	Use dates and COA type to assess confidence and risk. Update the mail piece and/or system of record. Use NCOALink® to confirm the COA remains active, especially for very recent moves. Prioritize by business value and risk tolerance.
MLNA (Moved, Left No Address)	Carrier or USPS records indicate the recipient moved and did not provide a forwarding address.	The person or business is no longer at that address; USPS does not know where they went.	Flag as high-risk for future mailings. Attempt contact via other channels (phone, email, digital). Rerun through NCOALink® in future cycles in case a COA is filed later.
BCNO (Box Closed, No Order)	A PO Box was closed or the rental was not renewed, and no forwarding order was filed.	Similar to MLNA, but specific to PO Boxes. The box is no longer valid, and no new address is available.	Treat like MLNA: pursue alternative contact methods, and rerun through NCOALink® over time to catch any new COAs.
Temporary Move	Recipient filed a temporary COA (generally 2 weeks to 6 months, with the possibility of a second 6‑month period). Used heavily in disaster situations. No new temporary address or end date is returned.	The person has filed a temporary forwarding order. Mail is being forwarded for a limited time, and some of these will later be converted to permanent moves.	Decide whether your mail needs to follow them temporarily. For operational/critical mail, plan to use other tools or channels to confirm where to send. Monitor for later permanent COAs via NCOALink®/ACS™.
NDA‑UTF (Not Deliverable As Addressed – Unable To Forward)	Forwarding orders have expired, or no valid COA exists. Carrier cannot deliver or forward the piece.	The address, for that recipient, is now a dead end. No active forwarding path remains within USPS rules.	Suppress or investigate before mailing again. Consider other channels to obtain an updated address.
ANK (Attempted, Not Known)	Neither the current resident nor the carrier recognizes the person’s name for that address.	The address itself is valid, but the name doesn’t belong there. Often reveals bad data entry or an old, unmaintained record.	Treat as a person‑level issue. Investigate data entry errors (wrong house number, wrong street, wrong unit). Consider alternative addressing (e.g., “Or Current Resident”) for marketing, or find the correct address via other sources.
IA (Insufficient Address)	Address is missing essential information needed for delivery, often secondary details like apartment, suite, or unit numbers.	Confirms that the carrier really does need the missing data; it’s not just a “nice to have.”	Combine with CASS™/DPV® results to pinpoint whether primary or secondary is missing. Go back to the source and collect complete address details before remailing.
NSN (No Such Number)	The primary (house or PO Box) or secondary (APT, UNIT, etc.) number does not exist.	Confirms CASS™ findings: the number you have is not valid at that location, and the carrier could not infer a correct alternative.	Prioritize correction. Investigate whether this is new construction (not yet in CASS™) or simply a bad number. Avoid remailing without correction; use other data sources and customer contact.
NSS (No Such Street)	The street name does not exist in that area. Commonly caused by ZIP or spelling errors.	Validates and extends CASS™ intelligence: you have a structurally wrong street‑and‑ZIP combination.	Check for typos in ZIP and street name. Compare against known customer information. Correct and revalidate with CASS™ before mailing again.
Vacant	Carrier has confirmed the address is unoccupied.	The location is currently vacant. For “Current Resident” / alternative addressing, this is a true dead end. For specific individuals, a COA or MLNA might be more appropriate but is not always used.	Suppress or treat cautiously for “Current Resident” mailings. Use Vacant signals together with CASS™ vacancy and NCOALink® results to decide whether to keep trying or shift strategy.
Deceased	Piece was delivered to the address; a current resident returned it marked that the addressee is deceased. USPS does not independently verify this status.	Serious indicator that the intended recipient has died, with both business and regulatory implications in some industries.	Treat with care. Review against internal records and regulatory requirements. Stop marketing mail. For regulated industries, follow your internal deceased handling and compliance procedures.
Refused	The addressee refused to accept the piece, often one requiring a signature.	The address and name are valid; the person simply rejected that specific mailing.	Examine why the piece might be refused (content, frequency, type). Other mailings to the same recipient may still be delivered.
Other codes (Outside Delivery Limits, In Dispute, Illegible, No Mail Receptacle, Unclaimed, etc.)	Indicate specific physical, operational, or ownership issues that prevented delivery.	The problem may be the delivery area, the receptacle, a dispute at the location, or something about the piece itself.	Investigate patterns. For one‑off cases, handle individually. For recurring issues (e.g., Illegible, No Mail Receptacle), adjust production, materials, or address capture processes.

All ACS™ reason codes ultimately fall into one of three buckets:

• An issue with the address,
• An issue with the person at that address, or
• An issue with the physical mail piece.

Recognizing which bucket you’re dealing with is the first step toward choosing the right response.

Short Notes on Nuanced Codes

Some ACS™ returns carry extra nuances that are easy to miss but have big implications. These are worth calling out.

1. COA with New Address: ACS™ COAs are similar to what you get from NCOA^Link®, but there are key differences:

• • ACS™ can provide information about COAs that just became effective, even while your mailing is still in process.

• • ACS™ will return some new addresses that NCOA^Link® cannot, including foreign addresses and new addresses that don’t yet validate as “good” in CASS™.
  • ACS™ can match to COA records that NCOA^Link® can’t. Many mailers see significantly more COAs when they combine NCOA^Link® and ACS™ than with NCOA^Link® alone.
  • With ACS™, you see how the COA was filed (Individual, Family, Business), plus both the Move Effective Date and the Made Available Date, which lets you gauge the stability and timing of the move.

These details help you decide how aggressively to update your system of record versus just the current mailing.

2. Temporary Move: Temporary moves are tricky because:

• • USPS forwards for a defined period (often 2–6 months, sometimes extended),
  • You don’t get the temporary forwarding address or the end date via ACS™, and
  • In disaster situations, Temporary COAs may later be replaced by Permanent ones.

As a result, how you handle Temporary depends heavily on your business model and the nature of your communications. For some operational or regulated mail, a temporary forward may not be sufficient.

3. Vacant vs. CASS™ Vacant: Vacancy timing matters:

• • In DPV^® / CASS™, an address is not flagged as Vacant until it has been vacant for at least 90 days and is not a rural route.
  • Via ACS™, a carrier can mark an address as Vacant on day one.

An ACS™ Vacant return can therefore:

• • Help you react much faster than DPV^® alone, and
  • In some cases, even tell you when to discount or ignore an older DPV^® Vacant result if the real‑world situation has changed.

4. Deceased

The Deceased code reflects a very specific chain:

• • The piece was delivered to the address on file.
  • A current resident returned it, indicating the addressee is deceased.
  • USPS generated an ACS™ record with the “Deceased” reason code.

USPS does not verify or manage any comprehensive “deceased” database. That has obvious business and, for some industries, regulatory implications. You should combine this signal with your internal data and policies before acting.

5. Illegible and Production‑Related Issues

Illegible, No Mail Receptacle, and some related codes often point back to production or design problems, not bad addresses. For example:

• • Windowed envelope windows cut slightly too low or too high, so key address lines don’t show.
  • Overly small fonts or poor contrast that can’t be read reliably.

Patterns of Illegible returns across many addresses in a single mailing should trigger a review of materials, layout, or print quality—not just address hygiene.

Structuring the ACS™ returns this way gives you two things:

• A quick reference so you can see, at a glance, what each code means and what to do about it.
• Enough nuance on the tricky codes to make decisions that go beyond “update or suppress” and actually improve your address quality strategy over time.

The Power of ACS™ Beyond CASS™ and NCOA^Link®

ACS™ provides information that neither CASS™ nor NCOA^Link® can give you, but only after you’ve actually mailed.

CASS™ can tell you an address is structurally valid, complete, and correct. If CASS™ indicates a house number is invalid, you don’t know why. Is it simply new construction that hasn’t made it into the database yet, or is it an address the carrier cannot resolve at all?

If you get an ACS™ return saying “No Such Number,” now you know. You should prioritize taking action on this address before mailing to it again.

If you do not receive an ACS™ record for that address, you can initially treat it as lower priority. Wait a couple of months to see if CASS™ begins validating the address, then you’ll know it was likely new construction. If it still doesn’t validate, you should take corrective action. The priority starts low but should increase over time.

Remember, if you can’t CASS™‑validate an address, you can’t check for many special address characteristics, and you also can’t make matches in NCOA^Link®.

NCOA^Link® can only supply COAs filed within the past 48 months. It returns new addresses only for permanent COAs where the new address is domestic, valid, and can be resolved to a single address.

ACS™ is limited to matching COAs from the last 18 months, but it can still:

• Identify some COAs that NCOA^Link® misses.
• Return new addresses, domestic and foreign, that NCOA^Link® cannot.
• Provide non‑delivery reasons that have nothing to do with a COA (for example, Vacant, Deceased, IA, ANK).

NCOA^Link® can be used to process and maintain your entire database and to ensure that a mailing meets the USPS Move Update requirement before it goes out the door. ACS™, by design, only flags information on the pieces you actually mailed after they’ve gone through the system.

Put simply, CASS™ and NCOA^Link® tell you what should happen based on USPS data, while ACS™ tells you what actually did happen, and that’s where the smartest decisions come from.

The Move Effective Date and Made Available Date in ACS™

Just as with NCOA^Link®, the dates associated with ACS™ returns can be of critical importance.

The Move Effective Date tells you when the person indicated they moved. In ACS™, this includes the specific day, not just the month and year as with NCOA^Link®. 

The Made Available Date tells you when the USPS made that COA information available to you.

Most of the time, these dates are the same or within a week of each other. But sometimes people file a COA late, with a Move Effective Date set weeks or months in the past and a Made Available Date that is much more recent.

Recently filed COAs also have a higher chance of being modified; for example, when a move is delayed or a Family COA was filed by mistake instead of an Individual COA. The Move Effective Date gives you the customer’s stated timeline, but the Made Available Date tells you when USPS actually processed the COA.

If you receive an ACS™ return with a new address and a very recent Made Available Date, consider whether to act immediately or wait briefly to see if the COA gets corrected. One way to do this is to monitor the COA through NCOA^Link® and confirm that it remains unchanged over time.

Combined with other factors, these dates help you assess how reliable the new address is and when to apply it, both to your next mailing and to your system of record.

What to Take Action On

Not every ACS™ return demands immediate action. You need to prioritize and manage based on need, risk, effort, and return.

For COA returns, evaluate the Move Effective Date and Made Available Date. Recent moves (within the last month) deserve some attention – especially if it is a Family COA.  Less than 0,001% of these get modified or corrected – and most of those corrections are within a week or two. Older moves are generally more stable. The question is whether to update the data in your system of record, or just on the mail piece.  

You can use NCOA^Link® to see if the COA is still active, being changed, and potentially returning the same information. It all depends on your risk factors and comfort level.

For Illegible returns, watch for patterns. If the same address repeatedly comes back illegible, that’s a red flag requiring investigation. Is something with the address or contents causing vital address information to not appear on the mail piece? If illegible returns appear across multiple different addresses in a single mailing, that might indicate a processing or printing issue rather than address problems.  For example, did you get a new batch of windowed envelopes where the window location is slightly different, causing some addresses to fail the tap test?

For ACS™ COA new addresses, CASS™ validation can give you an additional level of confidence and risk assessment. If the new address fails CASS™ validation, look closely at why it failed.

• • If the CASS™ failure indicates an invalid primary (house) number, it may simply be new construction that hasn’t been added to CASS™ yet. Even then, the piece should still reach the correct carrier for that street, who can often resolve delivery.
  • If the CASS™ failure indicates an invalid street name, it could be the first completed home on a brand‑new street, but more often, it means there is an error in the COA record itself, and a correction is likely coming. In that case, pieces will reach the right post office, but not the right carrier, which means a higher probability of ending up Undeliverable As Addressed (UAA).

By separating primary‑number failures from street‑name failures, you can treat some new addresses as “likely OK but watch,” and others as “high‑risk, prioritize correction.”

NOTE: When an invalid COA is filed, the recipient’s corrective action should be to first correct the COA from the old address to the correct new address.  They could also file a COA for themselves from the wrong new address to the correct new address.  However, if that wrong new address does not CASS™ validation to a certain level, that COA will not go into NCOA^Link®.

RECOMMENDATION: Whether a new address is from NCOA^Link®, ACS™, or direct from the recipient, there are multiple reasons to keep their prior address, especially when the new address has certain characteristics. Yes, that is more effort and data to store and maintain, but the tradeoff is the risk of losing contact with your customers.

Making Smarter Decisions by Combining Data Sources

We’ve already started to show that the real power comes from using ACS™ data in combination with CASS™ and NCOA^Link® results. The goal isn’t to treat each result in isolation, but to use them together to answer a better question:

Given everything we know about this name and address, what is the smartest thing to do next?

Let’s look at a few common scenarios.

Scenario One: CASS™ Fails DPV^® (N) – Is This Address Really a Problem?

An address fails CASS™ with DPV^® N (not confirmed). Is this critical?

1. 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. 
• If you have no prior ACS™ returns for this address, it might simply be new construction that hasn’t been added to the USPS database yet.

2. Decide how to treat it.

• You may choose to mail it (especially for marketing or lower‑risk pieces), watch for ACS™ results, and monitor whether CASS™ starts validating the address over the next few months. If it still doesn’t validate and ACS™ begins returning NSN, that address moves to the top of the corrective‑action list.

Here, CASS™ raises the question, and ACS™ helps you decide whether it’s a real problem right now.

Scenario Two: Missing Secondary Information – How Critical Is It?

CASS™ shows missing secondary information, for example DPV^® D with footnote N1. Does this matter? 

1. Check ACS™ history for that address. 

• If you have no prior ACS™ returns, the carrier has probably been able to deliver anyway. The address is not ideal, but it’s working for now. 
• If you have a prior ACS™ return showing “Insufficient Address” (IA) for that same address, the carrier is explicitly telling you they need the missing unit, apartment, or suite.

2. Act based on the combination.

• No ACS™ problems + CASS™ missing secondary: keep mailing, but put the record on a lower‑priority worklist to capture the missing information over time.
• ACS™ IA + CASS™ missing secondary: do not keep mailing blindly. Go back to the source and obtain the unit number or other missing detail before remailing, or use additional data services to fill the gap.

CASS™ alone can’t tell you whether the missing secondary information is truly blocking delivery. ACS™ confirms when it actually is.

Scenario Three: CASS™ / DPV^® Shows Vacant – But Is It Still Vacant?

CASS™ with DPV^® may show an address as Vacant. But what if someone just moved in?

1. Look for information related to that name at that address.

• Check NCOA^Link® results: does it indicate that person moved from that address?
• Check ACS™ history: do you have a Vacant return or a COA for that specific person at that specific address?

2. Interpret the pattern.

• If there’s an ACS™ Vacant for that person at that address, the vacancy was confirmed after they moved out. That’s a strong signal that the address is currently empty for your target.
• If there is no ACS™ return for that person at that address, they may have just moved in and the CASS™ vacancy flag is lagging behind reality. In that case, consider mailing with an ACS™ endorsement to let the carrier confirm the new status.

Remember, CASS™ vacancy is address‑based and delayed (at least 90 days for many addresses), while ACS™ is name‑and‑address‑based and can mark an address Vacant on day one. Combining the two gives you a better read on whether you should keep mailing, change strategy, or suppress.

Scenario Four: NCOA^Link® Near Match – Do You Mail or Suppress?

NCOA^Link® shows a near match or partial match but can’t provide a new address with enough confidence to return it. What do you do? 

1. Again, start with ACS™ history.

• Has ACS™ ever provided a new address for this person?
• Has ACS™ ever returned a non‑delivery reason (like ANK or IA) for them at the old address?

2. Choose a strategy based on your objective.

• If this is marketing mail, you might use alternative addressing (e.g., “Or Current Resident”) so you still reach someone at that location, even if you can’t be sure it’s your original target.
• If you need to maintain contact with that specific recipient, mail to the old address with an ACS™ endorsement and let the carrier break the tie. If the person has actually moved, you’ll get a new address in your ACS™ data. If they haven’t, the piece gets delivered.

This approach harnesses local carrier knowledge that CASS™ and NCOA^Link® simply do not have.

In each of these scenarios, the process is the same:

1. 1. Let CASS™ and NCOA^Link® surface the question. Is this address valid? Is there a COA? Is the address vacant? Is something missing?
   2. Use ACS™ history to ground that question in reality. What actually happened when you mailed to this name and address before?
   3. Make a decision that fits your business. Mail, suppress, correct, change addressing strategy, or use another channel.

Combining CASS™, NCOA^Link®, and ACS™ turns address quality from a set of disconnected checks into a unified decision system, one that helps you reduce waste, manage risk, and improve deliverability over time.

Time of Mailing Decisions

ACS™ data from previous mailings informs decisions about current and future mailings.

If prior ACS™ indicates an issue with the person at an address (like ANK, MLNA, or BCNO), that tells you the address itself is probably good. Consider using alternative addressing (like “Or Current Resident”) to ensure deliverability to whoever actually lives there now.

If you have an address where NCOA^Link® showed a near match or was unable to provide a new address, ensuring that you use ACS™ can help resolve the ambiguity and get you the new address while allowing the piece to still get delivered. 

The carrier’s knowledge, reflected in the ACS™ return, provides the information that NCOA^Link® could not.

Even if CASSTM validates the address and NCOA^Link® does not indicate a move,  ACS™ results from prior mailings can tell you when a piece is still likely not going to be deliverable for other reasons. Especially for marketing campaigns, you can choose to mail (a likely waste), suppress (perhaps missing some opportunities), or replace those records with other records that will have a higher deliverability rate and subsequent response rate.

Guide Corrective Actions

Different ACS™ reason codes should trigger different responses.

COA, MLNA, and BCNO returns suggest you should have an agent contact the person to confirm or obtain the new address. Don’t just update and forget. Use this as a customer service touchpoint. You can further prioritize the records to work on by the Move Effective Date. Prioritize the older ones first.

For MLNA and BCNO situations, rerun NCOA^Link® in the future. Sometimes people file a COA weeks or even a few months after they actually moved.

For Insufficient Address returns, use them in combination with CASS™ results. The ACS™ return confirms you need more information, CASS™ can guide you to what information (primary or secondary data, or even a completely different address). Go back to the source and request the complete mailing address.

For ANK returns, recognize that the address is valid but the person isn’t there. This might be a data entry error in the address, or it might indicate the person has moved a long time ago. Different responses are appropriate for each scenario.  There are other data sources that maintain COA’s longer than the USPS.

Using ACS™ for Risk Management

ACS™ data is invaluable for fraud prevention and PII (Personally Identifiable Information) protection.

High-risk addresses can be flagged and handled through alternative processes. For example, instead of mailing sensitive documents to a risky address, mail a postcard with ACS™ at a lower cost. The postcard contains no PII, allowing the USPS to dispose of it if undeliverable with no risk to you.

• Option one: The postcard says, “We are attempting to send you important information. Please contact us to confirm your address information.” If it comes back through ACS™ as undeliverable, you’ve verified the address issue without exposing sensitive information nor incurring the cost of the full piece.  
• Option two: The postcard says, “Your XYZ is on the way and should arrive shortly.” Utilize ACS™ on this postcard. If ACS™ returns it as undeliverable, initiate processes to contact and obtain corrected address information. If no ACS™ return occurs, assume successful delivery and mail the actual document.

With either option, the savings from sending fewer high-risk PII pieces more than cover the cost of sending the postcards, and you reduce the risk of PII getting into the wrong hands while maintaining customer service quality.

Performance Measuring

ACS™ data enables sophisticated performance measurement and continuous improvement.

• Measure deliverability rates by list provider or source. Are certain vendors consistently providing better quality addresses than others? Use that information in future purchasing decisions.
• Measure deliverability rates by address quality level or indicator. How do recent COAs perform versus older ones? What’s the deliverability rate for addresses with missing secondary information versus those with complete information?
• Measure deliverability rates by address characteristics. NoStats addresses, drop addresses, and addresses with no secondary information all perform differently. Understanding these patterns helps you make better decisions.
• Track deliverability rates by specific segments. In my experience, when mailing to small businesses using alternative addressing, NoStats drop address can see 40% undeliverable rates, and even higher when secondary information is missing. But that might still be acceptable if the response rates justify the waste.

Use these measurements to customize future name and address orders. If you know certain list characteristics correlate with poor deliverability, you can specify different criteria in your next purchase.  Conversely, if you find a combination of address types and status that have a higher response rate, you can specifically prioritize those in future data requests.

Continuous improvement becomes possible.

Physical Returns and Hardcopy Notices

ACS™ provides information back to mailers quickly and in an electronic format.  Yes, mailers can still elect to get physical pieces back or (in some cases) hardcopy notices.

NOTE: Hardcopy notices are expensive to both the USPS and mailers. This is why the USPS has started eliminating the use of this option. Effective July 2023, the USPS eliminated full-service hardcopy Address Correction Notices (STIDs).

Compared to the ACS™ electronic notices, the physical returns and hardcopy notices can take days to weeks longer to get back to a mailer. The mailer must then process the information from the pieces into their system, which takes time and introduces errors.

Getting ACS™ electronic notices, allows mailers to get the data faster, in a format ready for automated processing to update records, suppress records, and/or initiate appropriate corrective actions based on the nature of the delivery issue.  

Plus, using ACS™ of First Class mail allows the mailer to use the USPS Secure Destruction program.

Why ACS™ Remains Underutilized

Given its value, why do so many mailers fail to use ACS™ data effectively? Here are the most common reasons:

• There’s a knowledge gap. Many people don’t understand what ACS™ is or how it differs from CASS™ and NCOA^Link®.
• There’s a perception that ACS™ is expensive or complicated. In reality, for almost all Full Service mailers, they qualify for ACS™ data free of charge from the USPS. The cost is in setting up processes to capture, manage, and apply the data, but that cost is minor compared to the value.
• There’s an organizational challenge. ACS™ data needs to flow back into databases, customer service systems, and operational processes. This requires cross-functional coordination that many organizations haven’t established. But there are service providers that can do this for the mailer.
• Many mailers work with service providers who run CASS™ and NCOA^Link® but don’t provide comprehensive ACS™ data management. The data gets lost in the shuffle.

Specific to marketing mailings, “We buy in a list for one-time use, so there is no value to the updates from ACS™.” 

• ACS™ lets you know the quality of the addresses being provided by different list providers.  
• With each list purchase, you are likely using similar selection criteria. So, you could get the same record multiple times.  ACS™ data from prior mailings tells you which records in the new list should not be used.  
• If you purchased a list for a multi-mailing campaign over several weeks or a few months, ACS™ from the prior mailings allows you to be more efficient with the current and later mailings.

For Full-Service mailers, ACS™ data is often available at no additional USPS charge. The real investment is in the process, and the ROI is substantial.

Working with Service Providers

When evaluating mail service providers or address quality companies, ask specifically about ACS™ capabilities.

Almost all will support using a STID to activate ACS™, and have the USPS send the data to you.

But, do they offer to capture and return ACS™ data to you in a usable format? Do they help you interpret ACS™ reason codes and make decisions? Do they integrate ACS™ data with CASS™ and NCOA^Link® results? Will they help you apply ACS™data to future mailings? Do they provide trending and analysis over time?

At GrayHair Software, we treat ACS™ as a core component of address quality strategy, not an afterthought. We help clients set up efficient processes for obtaining ACS™ data, provide detailed analysis of ACS™ returns in combination with CASS™ and NCOA^Link® results, and guide specific corrective actions based on the complete picture.

The Bottom Line

CASS™ and NCOA^Link® are the primary tools to ensure qualification for postage discounts. They’re foundational. 

But ACS™? ACS™ is what separates organizations achieving modest deliverability improvements from those achieving best-in-class results. ACS™ closes the loop. It provides real-world feedback from the USPS equipment and carriers that actually handle and attempt delivery. It identifies issues that CASS™ and NCOA^Link® cannot. It enables continuous improvement of address quality over time.

For any recurring or multiple mailing campaign, ACS™ isn’t just beneficial. It’s an absolute must.

In the next article, we’ll explore how to connect these dots, how to use CASS™, NCOA^Link®, and ACS™ together to make smarter decisions at every stage of the address quality lifecycle. Because having the tools is one thing. Using them together strategically is what delivers results.

Until then, if you’re not using ACS™ data, you’re flying blind. You’re mailing, hoping for the best, but not learning from your results. And in an environment where deliverability matters more than ever, hope isn’t a strategy.

Next in this series

• Making Smarter Decisions: How to Connect CASS™, NCOA^Link®, and ACS™
• 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.