ACS™ vs. NCOALink®: What’s the Difference?

By Adam Collinson

If you’ve been in the mailing world for more than five minutes, you’ve heard two acronyms tossed around: ACS™ (Address Correction Service) and NCOA^Link® (National Change of Address). Both are critical tools for managing undeliverable-as-addressed (UAA) mail, but they work in different ways and at different times.

Think of it like this:

• NCOA^Link® is the pre-vacation checklist to a first-time destination: do what you can to make sure addresses are current before departure to try to ensure a successful trip.
• ACS™ is your prior trip journal and reviews from prior travelers: telling you what really happened after the mail entered the USPS system to ensure better, successful future trips. Here’s what you need to know about the differences, the overlap, and why the best strategy is to use them together.

Why These Tools Matter

UAA mail costs businesses billions each year in wasted printing, postage, lost opportunities, and customer frustration. It also costs USPS in handling and processing. Both ACS™ and NCOA^Link® were designed to enable mailers to reduce that waste:

• NCOA^Link® updates addresses before mailing by comparing your list against USPS’s change-of-address database.
• ACS™ provides feedback after mailing, showing what happened to undelivered pieces and why.

Neither is optional if you’re serious about deliverability and compliance. The real question isn’t “Which one?” but “How do they work together?”

Side-by-Side Comparison: ACS™ vs. NCOA^Link®

 

Feature	NCOALink®	ACS™
Timing	Pre-mailing	Post-mailing
Move Update Requirement	Yes – qualifies for USPS move update requirement	Yes – qualifies future mailing if used routinely and consistently
Change-of-Address Coverage	New addresses for most permanent moves to Domestic addresses (flag moves with no new address, some levels flag temporary COAs)	New address for permanent moves to Domestic and Foreign addresses (flag  moves with no new address and temporary COAs)
Non-COA Issues	None – only provides move updates	Yes – includes Nixie codes for reasons like insufficient address, illegible, deceased, etc.
Foreign Addresses	Identifies a foreign move but does not provide the new address	Provides a new foreign address when available
New Address Data	Only validated addresses, but Encoded (sometimes not translatable)	Plain-text, not limited by encoding (but may include invalid “garbage” addresses)
Match Logic	Very strict; requires high confidence in a match	Starts strict (PARS), then allows for carrier input for common-sense matches
Data Freshness	For Service Providers: Built weekly; 1-2 weeks old	Uses the most recent USPS information available
Data History	18 or 48 months (depending on licensee)	18 months

 

When NCOA^Link® Works Best

• 3rd Party Lists: any time you are not in control of the capture and maintenance of the list
• • • Large marketing mailings. Clean the purchased list before you send, so fewer pieces bounce in the first place.

• Client lists. Your business receives periodic lists from your clients – such as a company employee and retiree list to be covered by services.

• Ongoing customer communications. Regular NCOA^Link® processing keeps your database current with permanent moves – especially when you do not mail to all records on a regular basis.
• Compliance. NCOA^Link® is the go-to tool for demonstrating you’ve met USPS move-update requirements – as it applies to mailing done with the processed list.

When ACS™ Works Best

• Compliance.  Using ACS™ on a mail piece does not qualify that piece as meeting the USPS move-update requirement. It qualifies any pieces sent to the same name and address in the subsequent 95 days – so, good for monthly or quarterly statement mailings.
• Capturing what you couldn’t catch earlier. Matches NCOA^Link® could not make or could not return the new address, flag Temporary moves, new foreign addresses, and recent COAs filed after your last ran NCOA^Link®.
• Understanding why mail failed. Nixie codes reveal other issues unrelated to moves, like:
• • • Change of Address: person moved and is no longer at the address you have
    • 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)
  • Visibility.

• First-Class Mail.  Without ACS™, no immediate visibility to new addresses NCOA^Link®  cannot provide.  Depending on timing, mailers may be forced to extreme measures to get the new address or simply loose that contact

• Marketing Mail. Default USPS handling is that UAA mail is disposed of – with no feedback to the mailer.  Feedback allows marketers to determine such things as the quality of various list sources, the true response rate of delivered pieces, or at least, what to suppress or replace in future mailings.

• Process monitoring. ACS™ helps spot process and production errors quicker – when there is a sudden change to the rate and type of ACS™ codes – as well as when numbers are outside of industry averages.
• Reducing return-mail handling. Electronic notifications from ACS™ mean getting the data sooner and ready for further processing – save the time, cost and risk of managing physical returns.

Why You Need Both

Relying on only one tool leaves major gaps:

• NCOA^Link® without ACS™ means you are missing out on some Changes of Address and may never see the real-world outcomes.
• ACS™ without NCOA^Link® means you may not be meeting the move-update requirement and you’re always cleaning up after the fact. You incur waste, delays, lost opportunities, and risks that could have easily been avoided.

The smartest mailers treat these tools as complementary. NCOA^Link® gets you as close to correct as possible before the drop; ACS™ closes the loop afterward with reality checks and detailed feedback.

Practical Tips for Using Both Together

1. Run NCOA^Link® regularly to keep your list clean and compliant.
2. Run NCOA^Link® at the time of mailing to get the latest information.
3. Set up ACS™ with tracking in the IMb so you can connect feedback to individual mailings.
4. Monitor ACS™ data for trends (e.g., repeated “insufficient address” codes may point to database gaps or capture errors).
5. Use Delivery Point Validation (DPV) and other indicators to detect scenarios and direct corrective actions, such as what to do with potentially bad “new” addresses returned by ACS™.
6. Incorporate both tools into your best practices and compliance documentation: USPS wants to see routine, consistent processes.  Many industries require address quality and compliance related processes.

So, ACS™ or NCOA^Link®?

If you’re asking “ACS™ or NCOA^Link®?” you’re asking the wrong question.

Truth is, you need ACS™ and NCOA^Link®.

And the real question is, “For my business needs, how do I make the best use of ACS™ and NCOA^Link®?”

One is a pre-trip safeguard; the other is a post-trip report. Used together, they reduce waste, improve compliance, and give you the full picture of your address quality and mailing operations.

 

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.”