USPS Publication 28, formally titled “Postal Addressing Standards,” is the definitive reference for how addresses should be formatted, structured, and validated in the United States. Think of it as the Rosetta Stone for anyone dealing with address data.

In this article, I’ll explain what CASS™ actually does, why it matters, and most importantly, what all those cryptic codes in your CASS™ reports are trying to tell you. Because those codes aren’t just technical noise. They’re decision-making tools.

I once worked with a marketing director who was frustrated that NCOALink® kept “deleting” her best customers. When I asked what she meant, she explained that every time they ran NCOALink®, thousands of records got flagged with moves, and her mail counts dropped significantly.

Here’s a scenario I see more often than not: A mailer runs CASS™, processes through NCOALink®, 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.

Address quality best practices isn’t about running each process in isolation. It’s about connecting the dots between CASS™, NCOALink®, and ACS™ data (all of the data) to make smarter decisions at every stage. Let me show you how.

Address quality isn’t a single process. It’s a lifecycle that begins the moment an address enters your system and continues through database maintenance, just-in-time processing, mailing, and return mail handling. Excellence at one stage means nothing if you’re failing at another.

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™, NCOALink®, and ACS™. They’d improved their data entry processes. They’d done everything right.