Why Your Mailing List Goes Bad (and What to Do About It)

If you've been using the same mailing list for more than a year without cleaning it, you're almost certainly wasting money. The average mailing list loses 20–25% of its accuracy every year — not because of anything you did wrong, but because people move, businesses close, and addresses change. Here's what's happening to your list and what you can do about it.

The Numbers Behind List Decay

According to USPS data, approximately 40 million Americans move every year — about 14% of the population. That's the primary driver of list decay. But moves aren't the only reason addresses go bad:

Residential moves — the most common cause; USPS only retains change-of-address records for 48 months
Business closures and relocations — B2B lists decay faster than consumer lists because business churn is higher
Deaths and household changes — the person you're mailing to may no longer be at that address
Address standardization errors — "St" vs. "Street," missing apartment numbers, incorrect ZIP codes — these pieces get delivered to the wrong address or returned
New construction and address changes — USPS periodically updates delivery point codes as new addresses are added

How Fast Does a List Go Bad?

Here's a rough model based on industry data and USPS move statistics:

0–3 months old: approximately 1–2% undeliverable
6 months old: approximately 3–5% undeliverable
12 months old: approximately 6–10% undeliverable
18 months old: approximately 10–15% undeliverable
24 months old: approximately 15–20% undeliverable
3+ years old: approximately 25–35% undeliverable

On a 5,000-piece First-Class mailing with a 12-month-old list, that's 300–500 pieces — and $234–$390 in postage — wasted before a single piece is read. On a 20,000-piece Marketing Mail campaign, the numbers get much larger.

What NCOA Processing Does

NCOALink (National Change of Address) is a USPS-licensed database of permanent change-of-address records filed in the past 48 months. When we run your list through NCOA, we match your records against this database and update addresses where a match is found.

NCOA is the single most impactful list cleaning step for consumer lists. It catches the largest category of undeliverable addresses — people who moved and filed a change-of-address form with USPS. It doesn't catch everything (only about 50–60% of movers file a COA form), but it's the foundation of any list cleaning process.

What CASS Certification Does

CASS (Coding Accuracy Support System) is a USPS program that standardizes and verifies address formatting. CASS processing corrects common address errors — wrong street abbreviations, missing directionals, incorrect ZIP+4 codes — and assigns a Delivery Point Code (DPC) to each address. CASS certification is required to qualify for USPS automation discounts.

What DPV Validation Does

DPV (Delivery Point Validation) goes one step further than CASS: it checks whether the specific address actually exists in the USPS delivery database. An address can be correctly formatted (passing CASS) but still not be a real deliverable address. DPV catches those cases and flags them for removal or correction.

What About Duplicate Removal?

A fourth step — duplicate detection — removes records where the same person or household appears multiple times in your list. Duplicates waste postage and annoy recipients. We identify duplicates at the name, address, and household level and remove them before processing.

How Often Should You Clean Your List?

The standard recommendation is to clean your list before every major mailing, or at minimum once per year. For high-frequency mailers (monthly or more), quarterly cleaning is more cost-effective. The cost of cleaning — approximately $0.05 per record for full NCOA + CASS + DPV service — is almost always recovered immediately through postage savings on the first mailing after cleaning.

Get a Free List Analysis

Mail Movers offers a free list analysis for Delmarva businesses. Send us a sample of your list and we'll estimate the undeliverable rate and projected postage savings from cleaning. No commitment required.

Learn more about our list cleaning services → or call 410-749-1885.