Mail that doesn’t reach its destination is more than a nuisance — it’s a drain on budgets, time, and customer trust. Fortunately, USPS’s Address Correction Service (ACS™) is designed to shed light on why pieces go undelivered and how to prevent it from happening again.

Whether you’re sending millions of statements, marketing postcards, or compliance notices, ACS™ can uncover the root of common delivery problems and give you the data to fix them. Let’s look at five of the most frequent mail headaches ACS™ helps solve.

1. Customers Move — But You Don’t Know Where

The problem: People move. A lot. Every year, millions of Americans file change-of-address (COA) requests with the USPS. But, some do not file a COA. If your database doesn’t keep up, you’re mailing to empty homes and outdated addresses.

Without ACS™, on COA’s, some First-Class mail is simply forwarded and Marketing mail is disposed of – with no notification back to the mailer – often causing additional future waste and even lost customer contact.

How ACS™ helps: ACS™ delivers updated COA information after the mailing. Unlike NCOALink® (which works pre-mail), ACS™ can make additional matches and returns new permanent domestic addresses as well as new foreign addresses and flags temporary moves. That means you don’t just know that someone moved — you often get their new address, the effective date of the move, and if just an individual that moved or the whole family.

The win: Less wasted mail, more accurate customer records, and compliance with USPS’s move-update requirements.

2. Undeliverable-As-Addressed (UAA) Mail

The problem: Sometimes a piece can’t be delivered — not because of a move, but because the address itself is deficient or invalid. Think: a missing apartment number, an incomplete street name, or a typo in the ZIP Code. The result? UAA mail that goes nowhere.

How ACS™ helps: ACS™ provides Nixie codes — specific reason codes that explain why mail bounced. For example:

• I = Insufficient as addressed (missing details like apartment number)
• Q = Not deliverable as addressed – unable to forward
• A = Attempted not known (person not associated with that address)

The win: Instead of scratching your head over “return to sender” piles, you get actionable reasons to guide efforts to clean and improve your list.

3. Returned Mail That Piles Up in the Office

The problem: Handling physical returns is expensive. First, you have to wait for the physical returns. Then, someone has to open envelopes, interpret yellow labels, update databases, and shred or store the pieces. That’s time, labor, and compliance risk (especially if sensitive information is inside). And it is error prone.

How ACS™ helps: With electronic notifications, you bypass most of that manual work. ACS™ reports come directly to you, often before the physical piece makes its way back. If you opt into USPS’s Green & Secure program, undeliverable pieces can even be securely destroyed instead of sent back — saving handling costs and reducing the risk of lost or exposed data. Plus, you get the USPS’s UAA reasons codes to automate direction of the data to corresponding resolution activities.

The win: Less paper clutter, fewer manual errors, and stronger information security.

4. Mystery Issues and Process Issues

The problem: Sometimes the issue isn’t the customer — it’s your process. The USPS’s UAA reason indicates an address deficiency, but your data shows the address is complete. Maybe barcodes aren’t unique, apartment fields got cut off in printing, or whole regions of addresses show higher bounce rates. Without visibility, you’re stuck guessing.

How ACS™ helps: By tying feedback to the Intelligent Mail Barcode (IMb), ACS™ makes it possible to trace problems back to the original mailing run and connect with other address quality data. If you see validated addresses with repeating “illegible” or “insufficient address” codes, it may point to production quality issues. If a cluster of addresses consistently fails, it could be a systemic database gap.

The win: Instead of operating blind, you can spot trends and fix root causes — whether in data entry, printing, or list segmentation. Additionally, with deficient addresses, ACS™ allows you to prioritize correction efforts on records where the USPS carriers and clerks cannot figure out a correct delivery location.

5. Rising Costs from Undeliverable Mail

The problem: UAA mail is a lose-lose. You pay to print and mail pieces that never reach their target, and USPS pays to process and handle them. Those costs add up fast — and they ripple through to postage rates over time.

How ACS™ helps: By reducing undeliverable mail, ACS™ lowers both your direct costs and the burden on USPS. In fact, ACS™ is one of the few tools that benefits both the mailer and the postal service. Over time, consistent use can help improve compliance scores and may indirectly support lower overall industry costs.

Additionally, using ACS™ allows First-Class mailers to use Secure Destruction which further reduces mailers and the USPS’s handling costs.

The win: Dollars saved. Less waste. More sustainable mailing.

The Bigger Picture

ACS™ doesn’t prevent every issue — but it makes the invisible visible and provides guidance. Instead of treating undeliverable mail as an unavoidable cost of doing business, you get data, trends, and answers. Paired with pre-mail solutions like CASS™ and NCOALink®, ACS™ gives you a full-circle strategy: clean lists before sending, then learn from real-world delivery results to keep improving.

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.”