The #1 Rule in Address Quality: Nothing is 100% (And Why That’s OK)

By Adam Collinson

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

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Early in my career, I spent hours explaining to a client why their deliverability would never reach 100%, no matter how much they invested in address quality. 

They were frustrated. They’d implemented CASS™, NCOA^Link®, and ACS™. They’d improved their data entry processes. They’d done everything right. 

And still, about 1% of their mail came back undeliverable.

“What are we paying for if we can’t get to 100%?” they asked.

That question reveals a fundamental misunderstanding of address quality, and I see it regularly, even after 25 years in the postal industry.

So let me be direct: You will never achieve 100% deliverability. More importantly, you shouldn’t try. Here’s why.

The Reality of Address Data

Address-related data, information, and handling involves over 300,000 mail carriers across the United States. Each carrier has local knowledge about their routes and they make daily decisions about how to record address information and how to handle addresses with unusual characteristics or missing information.

This human element introduces inherent variability that no database can fully capture. What one carrier knows about a particular address might not be documented anywhere. How one carrier interprets incomplete information might differ from another carrier’s interpretation.

Only about 60% of addresses have no special characteristics. 

Let that sink in. 

Over one-third of all addresses in the United States have something unique, unusual, or exceptional about them that will be of interest to some mailers and their business operations.

When information is presented, and standards are referenced, they typically focus on the 90% scenario, the general case. The documentation covers what usually happens, how things typically work. But in reality, there are exceptions. And often, there are exceptions to the exceptions. And in some cases, there are even exceptions to the exceptions to the exceptions.  

Add constant change to the mix, and you start to understand the challenge. New construction addresses get added. Streets get renamed. ZIP Codes get realigned. Businesses move. People relocate. The address ecosystem is dynamic, not static.  The USPS receives over 100,000 Change of Address (COA) requests a day.

This brings us to the number one rule in addressing: nothing is 100%.

Why “It Depends” Is a Valid Answer

Many answers in address quality start with “It depends.” This frustrates people looking for simple, definitive rules. But “it depends” isn’t a cop-out. It’s reality.

Does an address that fails CASS™ validation need to be suppressed? It depends. Is it a new construction whose data is not yet available via CASS™, but carriers are already delivering to the address? Or is there a simple issue with the address that the Carriers can easily resolve and complete delivery? Or is it a genuinely invalid address that will never be deliverable? Prior ACS™ data provides context, but even that isn’t always definitive.

Should you mail to an address flagged as vacant? It depends. Has someone moved in recently but the carrier hasn’t updated the status? Or is it genuinely unoccupied? NCOA^Link®  and prior ACS™ results for that specific person at that address inform the decision, but may not guarantee an outcome.

Does missing secondary information matter? It depends. Can the carrier figure out delivery without a unit number based on other information? Or is the secondary information critical? Past delivery success provides guidance, but circumstances change.  Delivery may depend on which Carrier is delivering on that route that day.

“It depends” recognizes that address quality isn’t about applying rigid rules. It’s about making the best informed decisions considering multiple factors, understanding that even good decisions won’t always yield perfect results.

The Law of Diminishing Returns

There’s a point where additional investment in address quality provides minimal improvement. Understanding where that point lies for your organization is critical. But even that decision needs to be re-evaluated over time. Again, things change over time: the issue gets worse, the solution gets cheaper, or a new solution becomes available.

Moving from 10% undeliverable to 5% undeliverable might require modest investment in basic processes like CASS™ and NCOA^Link®. Moving from 5% to 2% requires more sophisticated approaches like systematic ACS™ data utilization and decision engines. Moving from 2% to 1% demands comprehensive lifecycle management and continuous improvement processes.

Now, moving from 1% to 0.5%? That might require disproportionate investment for marginal gains. And moving from 0.5% to 0%? Effectively impossible and certainly not cost-justified.

Different organizations have different optimal points. An organization mailing time-sensitive operational documents might justify investment to reach 0.5% undeliverable. A marketing mailer with generous margins might optimize at 2%.

Volume also matters.  In many cases, the solution implementation is a fixed cost. So, it may not be worth it to one mailer where it impacts 1% or their 1 million records (so 10,000 pieces). However, for another mailer where the impact is only 0.5%, but on 10 million records (so 50,000 pieces), the cost may be justified.

The key is understanding your specific economics and making rational investment decisions. Perfectionism isn’t a strategy. It’s a waste of resources.

Managing Expectations Internally

One of the most important aspects of address quality management is setting appropriate expectations with stakeholders.

When presenting address quality improvements to leadership, avoid suggesting you’ll eliminate all undeliverable mail. Instead, frame it as moving from current performance toward best practice benchmarks.

“We’re currently at 8% undeliverable. Best practice organizations achieve 2% to 3%. Our goal is to reach 4% within 12 months and then evaluate next steps.” That’s realistic and achievable and sets the understanding that this is not a one-and-done, but a continuous improvement process.

Contrast that with: “We’re implementing address quality improvements to eliminate undeliverable mail.” Literally, the only way to eliminate all undeliverable or return mail is to not mail at all. To suggest otherwise sets an expectation you cannot meet, which undermines credibility when results inevitably fall short.

Educate stakeholders about the inherent variability in address data. Help them understand that some undeliverable mail is the cost of doing business in a dynamic environment with imperfect data sources.

Frame address quality as continuous improvement rather than problem elimination. The goal is systematic progress toward better results, not perfection.

CASS™ itself is an excellent example of continuous improvement. We are currently on Cycle O requirements. Each CASS™ cycle improves net accuracy. But improvement at scale always creates edge cases. That’s the nature of complex systems.

It is about continuous improvement.

Making Decisions Under Uncertainty

If nothing is 100%, how do you make good decisions?

The answer is risk management. You assess probabilities, evaluate costs and benefits, and make informed choices knowing that outcomes aren’t guaranteed.

An address with multiple risk factors (recent CASS™ validation failure, no prior delivery history, flagged as high-risk type) might have a 50% chance of being undeliverable. Do you mail it? That depends on the cost of mailing versus the potential value if it delivers. Sometimes you mail high-risk addresses because the payoff justifies the risk.

An address with good validation, clean delivery history, and no risk flags might have a 98% probability of successful delivery. Do you mail it? Almost certainly yes. But recognize that 2% chance of failure exists.

This probabilistic thinking is how best practice organizations approach address quality. They don’t seek certainty. They seek favorable odds and make peace with occasional unfavorable outcomes.

Building Resilient Systems

If you can’t achieve 100% deliverability, you need systems that work despite imperfect results:

• Build redundancy into critical communications. If something absolutely must reach a customer, use multiple channels. Send mail, but also send email. Make phone calls. Use text messages. Don’t rely solely on a single address delivery.
• Create exception handling processes. When mail comes back undeliverable, what happens? Is there a defined workflow for investigating, contacting the customer, and resolving the issue? Exception handling is where many organizations fail, not in the primary processes.
• Implement monitoring and alerting. If undeliverable rates spike suddenly, you need to know quickly. Sudden changes might indicate processing errors, list quality issues, or operational problems that require immediate attention.
• Design customer experiences that accommodate address issues. If someone’s mail doesn’t arrive, can they easily log into a web portal and access the information another way? Can customer service quickly identify and resolve address problems?

If you know an address has an issue or has restriction of filing a change-of-address, do your systems and processes make the person aware and direct them on what to do? For example:

• This address requires secondary address information (APT, STE, UNIT…). Please add this information.
• Change-of-address is restricted from this address. Please provide another form of contact (email, phone, or alternate address).
• This address is in an area where the USPS indicated mail delivery is not performed to the physical addresses. Please provide your PO BOX address used for receiving mail.

Resilience isn’t about preventing all failures. It’s about handling failures gracefully when they happen.

The Value of Marginal Improvements

Just because you can’t reach 100% doesn’t mean improvements lack value. Every percentage point of improvement has real economic impact.

An organization mailing 100 million operational pieces annually at $1.00 per piece spends $100 million on mail. Reducing undeliverable rates from 3% to 2% has a value of $1,000,000 annually. Reducing from 2% to 1% saves another $1,000,000.

But the value extends beyond postage savings. Improved deliverability increases response rates, improves revenue flow, enhances customer satisfaction, reduces customer service inquiries, improves regulatory compliance, and decreases fraud risk.

Small improvements compound over time. An organization that consistently operates at 1% undeliverable versus 3% undeliverable creates cumulative advantages in customer relationships, operational efficiency, and financial performance.

Don’t dismiss marginal improvements because they don’t achieve perfection. Marginal improvements are where the value lives.

Learning to Love Exceptions

Since nothing is 100%, you’ll find exceptional situations regularly. The question is whether you treat exceptions as problems or opportunities.

Every exception teaches you something about address quality. Every unusual address that doesn’t fit standard patterns reveals something about how the postal system actually works versus how documentation says it works.

Exceptional addresses in places like Syracuse, Indiana (with all the EMS addresses) or Atlanta, Georgia (with all those Peachtree street name variations) remind us that addressing isn’t as standardized as we might like. Rural routes, alphas in address ranges, fractional house numbers, and countless other variations exist because addressing evolved organically across thousands of local jurisdictions.

Remember, the USPS provides guidelines on the creation of addresses, but, with the exception of PO BOX addresses, the USPS does not make the addresses. That is done by the local community or even the builder.

The organizations that excel at address quality don’t eliminate exceptions. They document them, understand them, and build processes that handle them appropriately.

When Perfection Becomes the Enemy

Perfectionism in address quality can actually harm results.

Organizations that suppress any address with any risk factor might improve their undeliverable rate slightly but miss significant numbers of deliverable addresses. The opportunity cost of over-suppression often exceeds the savings from reduced undeliverables.

Organizations that refuse to mail until every address passes every validation check might delay time-sensitive communications past their useful window. Perfect information that arrives too late provides no value.

Organizations that invest disproportionately in pursuing the last percentage point of improvement might starve other initiatives that offer better returns, such as increasing volume in a marketing mailing.

Perfectionism creates paralysis. It leads to over-engineering, excessive process, and diminishing returns. The goal should be awareness and continuous improvement, not perfection.

The Role of Judgment and Experience

If rigid rules don’t work and nothing is 100%, what’s the alternative?

Judgment and experience matter enormously in address quality. Knowing when to apply which processes, how to interpret results in context, and what decisions make sense for specific situations separates basic compliance from sophisticated address quality management.

This is why working with experienced partners provides value beyond simple execution. A partner who has seen thousands of address scenarios, encountered countless exceptions, and managed diverse situations brings judgment that can’t be captured in documentation or automated in software.

At GrayHair Software, we bring decades of collective experience across diverse industries and mailing scenarios. We’ve seen what works, what doesn’t, and what “depends” on specific contexts. That experience informs recommendations that go beyond rule-based compliance.

You can develop this expertise internally over time. But recognizing that expertise matters, and investing in developing or accessing it, is critical for achieving best practice results.

Embracing Uncertainty

The address quality professionals who achieve the best results are those who’ve made peace with uncertainty.

They understand that decisions will be made with incomplete information. They accept that some percentage of choices will yield unfavorable outcomes. They recognize that continuous improvement matters more than occasional failures.

They also realize that things change outside of their control. Data and processes change all the time. Therefore, best practices for your operations also change. Past decisions need to be periodically revisited.

This mindset shift from seeking certainty to managing probability is foundational. It enables risk-appropriate decision-making rather than defensive decision-making. It allows organizations to find their optimal points on the cost-benefit curve rather than pursuing an impossible level of perfection.

Embracing uncertainty doesn’t mean accepting poor results. It means understanding that good results include some level of failure, and that’s not just acceptable but inevitable.

The Framework for Good-Enough

So if 100% isn’t achievable, what should you aim for?

Best practice organizations achieve:

• 0.5% to 1% undeliverable on operational mail.
• Under 2% on consumer marketing mail.
• 5% to 8% on small business marketing mail.

These aren’t arbitrary numbers. They represent the performance levels achieved by organizations with comprehensive address quality programs, sophisticated decision-making processes, and continuous improvement cultures.

Can you do slightly better in specific scenarios? Sure. Will you do slightly worse in other scenarios? Probably. But these benchmarks provide realistic targets that justify investment and indicate genuine excellence.

If you’re significantly above these benchmarks, there’s substantial opportunity for improvement. If you’re at or below these levels, your energy might be better spent on other priorities than pursuing the last fraction of a percentage point, but “It Depends” on your volumes and the impacts.

Making Peace with Imperfection

Here’s what I tell clients who are frustrated by less-than-perfect results:

A 99% deliverability rate isn’t a failure. It’s an exceptional performance in a complex, dynamic environment with imperfect data and human variability.

The 1% of mail that doesn’t deliver isn’t wasted if you’ve built good exception handling processes. It’s information that helps you improve databases, refine processes, and serve customers better. This data may even identify new leads and opportunities for your organization.

The goal isn’t to never have undeliverable mail. The goal is to make informed, economically rational decisions that optimize results within realistic constraints.

Final Thoughts

Nothing is 100% in address quality. That’s not a limitation. It’s reality.

The organizations that struggle with address quality are often those seeking certainty and perfection. The organizations that excel are those that embrace probability and optimization.

They understand that “it depends” is a sophisticated answer reflecting genuine complexity. They recognize diminishing returns and invest accordingly. They build resilient systems that work despite imperfect data. They value marginal improvements while accepting that perfection is impossible. They develop judgment and experience rather than seeking rule-based automation. They make peace with uncertainty and focus on continuous improvement.

This mindset shift from perfectionism to pragmatism is perhaps the most important lesson in address quality management.

You’ve now read through this entire series on address quality. You understand why it matters, what tools are available, how to use them effectively, and what results to expect. You know about CASS™, NCOA^Link®, and ACS™. You’ve learned how to connect these data sources to make smarter decisions. You understand best practices across the complete lifecycle.

Most importantly, you understand that nothing is 100%. And that’s not just okay. It’s the starting point for building realistic, effective, economically rational address quality programs that deliver genuine business value.

The question isn’t whether you’ll achieve perfection. The question is whether you’ll achieve continuous improvement toward best practice benchmarks while making peace with the inherent imperfection of address data.

That is address quality excellence. Not perfection. Not certainty. But systematic, sustained progress toward better results despite unavoidable limitations.

And in a world where nothing is 100%, that’s the best possible outcome.

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If you have questions about address quality or want to discuss your specific challenges, I’m always happy to talk. You can reach me at acollinson@grayhairsoftware.com or connect with GrayHair Software at engage@grayhairsoftware.com.

Because while nothing is 100%, we can certainly help you get a lot closer to your optimal results than where you are today.