Undeliverable-as-addressed (UAA) mail is the classic double loss. You pay to print and send it; USPS pays to handle and process it. Best case, delivery is delayed and there are negative impacts.  Worst case, it never arrives – and nobody wins.

That’s why Address Correction Service (ACS™) is so powerful. Used well, it doesn’t just tell you what happened to your mail after the fact – it becomes a feedback loop that continually improves your address quality.

Here are some ACS best practices for ACS™ to reduce UAA mail, cut costs, and stay compliant.  Actual best practices will vary from mailer to mailer and even from mailing campaign to mailing campaign.

1. Always Pair ACS™ with NCOALink®

If ACS™ is your rearview mirror, NCOALink® is your headlights. One looks back, the other looks ahead. The USPS still requires move-update compliance, and the best way to meet it is by using both tools consistently.

• • NCOALink® cleans your lists before sending, reducing the amount of UAA mail due to permanent Change Of Address (COA). Pieces mailed within the subsequent 95 days from being processed via NCOALink® meet the move-update requirement to qualify for postage discounts.
  • ACS™ catches and returns additional COA information as well as other reasons why a piece was not deliverable.  Best case, this is post-mailing, activating ACS on a piece does not qualify that piece as meeting the move-update requirement.  It qualifies any additional pieces sent to the same name and address in the subsequent 95 days.

Best practice: Schedule regular NCOALink® database updates (monthly or quarterly, depending on volume), perform NCOALink® at the time of mailing to get the latest information, and use ACS™ on the pieces to get and feed back information into your system after every mailing.

2. Stick with Full Service ACS™ + SingleSource

There are multiple ACS™ “flavors” (Traditional, OneCode, Full Service). Each of these has its own data format and fulfillment methods.  But then a standard format (SingleSource) was made available across all “flavors”. Full Service ACS™ paired with SingleSource data is the standard. Why?

• • Cost savings: Full Service ACS™ is free if your mailings qualify.  Additionally, if >95% qualifies as Full Service, even the non-Full-Service pieces can receive ACS data for free.
  • Data simplicity: SingleSource consolidates feedback across all ACS™ types into one format, reducing processing complexity.

Best practice: If you haven’t qualified for Full Service yet, make it a priority. The ROI is immediate in additional postage discounts and reduced ACS™ fees.

3. Keep IMb Unique for 12–13 Months

The Intelligent Mail Barcode (IMb) isn’t just a tracking number. It’s the link between your mail pieces and ACS™ data.

Here’s the catch: USPS recommends keeping IMbs unique for 45 days, but UAA notifications can take much longer to surface. Industry experts recommend 12–13 months of uniqueness to ensure you can match late returns.

Best practice: Extend your IMb uniqueness window to at least one year. It prevents mix-ups and ensures long-tail ACS™ feedback is still traceable.

4. Learn to Interpret and Act on ACS™ Codes

ACS™ feedback is only valuable if you know what to do with it. The key? Understanding the codes.

• • COA codes (blank, G, K, W): These require address updates, investigation or suppression.
  • Nixie codes (L, Q, A, I, P,…): These point to non-move reasons:
    • Address Issues: missing apartment numbers, no such street, no mail receptacle,…
    • Person Issues: Person is Not Known at that Address (the name is good, the address is good, but that name/address combination is not good).
    • Mail Piece Issue: Illegible (printing or insert issue)

Best practice: Train your team on ACS™ codes and build workflows around them. For example, “I = Insufficient address” should trigger data capture reviews; “P = Deceased” should trigger immediate suppression.

5. Use ACS™ to Monitor Your Processes

ACS™ is more than address hygiene — it’s a diagnostic tool for your mailing operation.

• • Repeated “L = Not legible” codes? Printing quality issue.
  • Frequent “I = Insufficient address”? Your data capture process may be broken – or – only part of the address information getting pulled / printed on the actual mail pieces.
  • A spike in foreign moves? Your audience demographics may be shifting.
  • The rate of certain issues keeps increasing – your processes to address these issues are not working.

Best practice: Don’t just file ACS™ data and reports away. Review them monthly for trends and tie them back to operations, not just addresses.

6. Take Advantage of Green & Secure

Physical returns are a headache. They take longer to get and process, introduce data quality and compliance risk, and increase costs. USPS’s Green & Secure initiative allows mailers to choose to allow the USPS to dispose of UAA pieces instead of physically returning – including an option for secure destruction of First-Class UAA.

• • Saves USPS handling costs (good for long-term industry rates).
  • Reduces risk of sensitive data floating around in return mail processes.
  • Requires ACS™ to ensure that UAA information is provided back to mailers to prompt corrective actions for future mailings.

Best practice: Opt into Green & Secure for First-Class mailings where physical returns don’t add business value.

7. Validate “New” Addresses with DPV and other indicators

Not all addresses returned by ACS™ are clean. Some are “garbage” — they look like addresses but fail delivery validation. That’s where Delivery Point Validation (DPV) comes in.

The question is “WHY?”  Is it a new construction address that needs a month or two for the information to appear throughout the USPS’s data.  Or, is it invalid address information, which is likely to get corrected in the future.

Additionally, some addresses have special characteristics and many industries have restrictions on the types of addresses that are acceptable.  For those, it is important to evaluate the new addresses to determine if they can be accepted and/or if additional actions are required.

Best practice: Run all ACS™-provided new addresses through CASS with DPV before updating your database. This step can filter out invalid or unconfirmed new addresses as well as unacceptable and problematic new addresses.

8. Document for Compliance

USPS doesn’t want you to just activate ACS™; it wants you to use the data to positively impact future mailings.  Documenting how the ACS™ data is used matters, especially for large mailers who could be audited by the USPS and other compliance entities.

Best practice: Maintain records of:

• • When ACS™ data is received
  • How codes are processed
  • What changes were made to your database
  • Frequency of updates
  • Overall performance – how much and what type of ACS data are you seeing over time

Remember, mailing processes and operations are not static.  You may be able to control your own operations, but things also change within the USPS’s operations.  ACS™ data gives mailers the ultimate view into what is happening and when something has changed.  Then the question is – did something break that needs to be fixed, or did something change that now needs to be accounted for?

This not only demonstrates compliance but also shows continuous improvement and ROI on your address-quality program.

9. Integrate ACS™ Data Across Systems

The most efficient mailers aren’t treating ACS™ feedback as a one-off report — they’re combining it with other available information to focus actions and integrating it directly into CRMs, ERPs, and marketing databases.

For Example: ACS™ indicates a delivery issues like No Mail Receptacle or Insufficient address. CASS / DPV indicates a non-deliverable address – BECAUSE this is an R777/9 street address.  Now you know this is likely the physical street address of their home or business, but the USPS does not deliver mail to that address.  Instead, they have a PO BOX address for mail delivery.  So, you mark the address as a physical, non-mailing address and you initiate efforts to specifically ask for and obtain their PO BOX mailing address.

Best practice: Automate ACS™ data feeds into your main customer systems. This ensures address quality improvements flow everywhere, not just in mailing operations.

The Bottom Line

ACS™ is more than an after-the-fact mail report. Done right, it’s a compliance tool, a cost saver, a risk reducer, a lead generator, and a process monitor all rolled into one. Pair it with NCOALink®, qualify for Full Service, train your team on the codes, and use the data for continuous improvement.

The result: less waste, cleaner data, and fewer undeliverable pieces draining your budget and generating risks.

Want to explore further?

For more information about ACS™ Processing and Results, request a copy of Adam Collinson’s most recent presentation to the Central Illinois PCC: “ACS™ 101 – The Basics of ACS™ Processing and Results.”