What is USPS CASS Certification? Complete Guide for 2025
Everything you need to know about CASS certification - from understanding the basics to implementing CASS-certified address verification and saving up to 40% on postage.
Table of Contents
If you send mail in the United States - whether it's marketing materials, invoices, packages, or statements - you've likely heard of USPS CASS certification. But what exactly is it, and why should your business care?
In this comprehensive guide, we'll explain everything you need to know about CASS certification: what it is, how it works, who needs it, and most importantly, how it can save your business thousands of dollars on postage while improving delivery rates.
What is USPS CASS Certification?
CASS (Coding Accuracy Support System) is a certification program run by the United States Postal Service that validates address verification software meets strict accuracy standards for mail processing.
Established by USPS in 1991, CASS certification ensures that address processing software can accurately:
- Match addresses to the official USPS address database
- Standardize addresses according to USPS formatting rules
- Add ZIP+4 codes and carrier route information
- Validate that addresses are actually deliverable
To earn CASS certification, software must achieve at least 98.5% accuracy when tested against USPS sample databases. This certification must be renewed annually, ensuring that certified systems remain current with postal standards.
Why CASS Certification Matters
Save Up to 40% on Postage
CASS-certified addresses qualify for USPS presort discounts. Depending on mail class and volume, savings can reach 40% off standard postage rates.
Reduce Undeliverable Mail by 85%
Studies show CASS certification reduces mail returns by 80-85%. This means fewer wasted materials, lower reshipping costs, and happier customers.
Meet USPS Compliance Requirements
Bulk mailers must use CASS-certified address processing to qualify for presort rates. Without certification, you pay full postage prices.
Faster Mail Delivery
CASS-standardized addresses with carrier route codes enable automated sorting, getting your mail delivered 1-3 days faster.
How CASS Certification Works
The CASS certification process involves rigorous testing by USPS:
-
Vendor Application
Software provider applies to USPS and receives a test database containing sample addresses with known correct values.
-
System Testing
The provider processes all test addresses through their verification system, generating standardized output with ZIP+4, carrier routes, and delivery point codes.
-
Accuracy Evaluation
USPS compares results against known correct values, measuring accuracy across multiple criteria including address matching, ZIP+4 assignment, and carrier route coding.
-
Certification Issuance
If the system achieves 98.5% accuracy or higher, USPS grants CASS certification with a unique certification number valid for one year.
-
Monthly Database Updates
Certified providers receive monthly USPS database updates to ensure address data remains current. USPS adds, removes, and modifies thousands of addresses monthly.
-
Annual Renewal
Certification expires after one year and must be renewed through complete retesting to maintain compliance.
CASS Data Elements Explained
CASS-certified systems return several critical data elements beyond the standardized address:
| Data Element | Description | Example |
|---|---|---|
| ZIP+4 Code | Nine-digit ZIP code that identifies delivery area down to a city block or building | 94043-1351 |
| Carrier Route | Code identifying the specific mail carrier route for delivery | C909 |
| Delivery Point | Two-digit code identifying the exact delivery point within a carrier route | 00 |
| DPV Confirmation | Delivery Point Validation code confirming address exists and is deliverable | Y (confirmed), N (not confirmed), S (secondary missing) |
| Record Type | Indicates address type: S (street), H (highrise), F (firm), R (rural), P (PO Box) | S |
| Check Digit | Barcode check digit for automated mail sorting | 2 |
What is DPV?
Delivery Point Validation (DPV) is a USPS database that confirms whether a specific address is a valid delivery point. While ZIP+4 tells you the area, DPV confirms the exact address exists. A DPV code of "Y" means USPS can deliver mail to that address - this is the gold standard for address verification.
Who Needs CASS Certification?
CASS certification is essential or highly beneficial for these businesses:
Direct Mail Marketers
Save 20-40% on campaigns with presort discounts and reduce returned mail
E-commerce Companies
Reduce failed deliveries and improve customer satisfaction
Financial Services
Ensure statements and notices reach customers reliably
Publishers & Subscriptions
Qualify for periodical rates and reduce subscription churn
Healthcare Organizations
Ensure HIPAA-compliant communications reach patients
Government Agencies
Required for many government mailings and compliance
When is CASS Required?
CASS certification is required to qualify for USPS presort discounts on bulk mailings (500+ pieces). Without CASS-certified addressing, you'll pay full postage rates - potentially 40% more than necessary.
CASS vs Standard Address Validation
| Feature | Standard Validation | CASS Certified |
|---|---|---|
| USPS Certification | No official certification | Officially certified by USPS |
| Accuracy Requirement | Variable (typically 90-95%) | Minimum 98.5% accuracy |
| Database Updates | Irregular or quarterly | Monthly USPS updates required |
| ZIP+4 Codes | Often not provided | Always provided when available |
| Carrier Route | Not included | Full carrier route codes |
| DPV Validation | Usually not included | Delivery point confirmation |
| Presort Eligibility | Not eligible for discounts | Qualifies for presort discounts |
| Best For | Basic format checking | Bulk mail, compliance, savings |
CASS ROI: Calculate Your Savings
Let's look at real numbers. Here's what a company mailing 100,000 pieces monthly can save:
Monthly Savings Example
| Monthly mail volume | 100,000 pieces |
| Standard First-Class postage | $0.63/piece = $63,000 |
| CASS presort rate | $0.42/piece = $42,000 |
| Monthly Postage Savings | $21,000 |
| Returned mail reduction (3% to 0.5%) | $2,500 saved |
| Total Monthly Savings | $23,500 |
| Annual Savings | $282,000 |
Even for smaller volumes, the math works. A business mailing just 10,000 pieces monthly can save $2,000-$3,000 per month - that's $24,000-$36,000 annually.
How to Implement Address Verification
Sthan.io's Address Verification API standardizes addresses to USPS format and appends ZIP+4 codes. Note: Sthan.io is not CASS-certified. For presort mail discounts requiring CASS certification, you'll need a CASS-certified provider. Here's how to use Sthan.io for address verification:
Step 1: Get Your API Key
Sign up for free at Sthan.io. You get 100 free verifications per month - no credit card required.
Step 2: Make a Verification Request
curl -X POST https://api.sthan.io/v1/address/verify \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"address": "1600 amphitheatre parkway mountain view ca"
}'Step 3: Handle the Response
{
"status": "verified",
"confidence": 100,
"input": "1600 amphitheatre parkway mountain view ca",
"standardizedAddress": {
"addressLine1": "1600 AMPHITHEATRE PKWY",
"city": "MOUNTAIN VIEW",
"state": "CA",
"zipCode": "94043",
"zipPlus4": "1351",
"fullZip": "94043-1351"
},
"metadata": {
"latitude": 37.4224764,
"longitude": -122.0842499
}
}Understanding the Response
- standardizedAddress - Address formatted to USPS standards
- fullZip: "94043-1351" - Complete ZIP+4 for precise delivery routing
- confidence: 100 - High confidence in the verification result
- metadata - Geographic coordinates for mapping applications
Frequently Asked Questions
Related Resources
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Written by Sthan.io Team
The Sthan.io team specializes in address data infrastructure, helping businesses verify, standardize, and geocode addresses at scale. We're passionate about making location data accessible and affordable for developers and businesses of all sizes.
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