What is USPS CASS Certification?
CASS (Coding Accuracy Support System) certification is the United States Postal Service's test that address-matching software must pass to be used for automation and carrier route postage prices. Certification is valid until the end of the current two-year certification period, and software must score at least 98.5% in categories such as ZIP+4 and carrier route and 100% in others such as DPV. It is required to claim automation prices on mail; checking a customer address does not need it. sthan.io is not CASS-certified.
Last reviewed: September 29, 2026
Quick Definition
USPS CASS Certification (Coding Accuracy Support System) is an official validation that address verification software meets United States Postal Service standards for mail sorting accuracy and address standardization. CASS-certified systems must score at least 98.5% in some test categories (such as ZIP+4 and carrier route) and 100% in others (such as delivery point coding and DPV), and CASS-certified coding is required for mailings claimed at automation prices.
Understanding USPS CASS Certification
CASS Certification is the postal service's test for address-matching software in the United States. Established by the USPS in 1991, CASS checks that address processing software accurately matches addresses to the postal reference database and formats them according to postal standards. It is required for mailings claimed at automation prices and for carrier route coding; a high mail volume by itself does not make it required.
To achieve CASS certification, software vendors must submit their systems to rigorous testing by the USPS. The testing process evaluates accuracy against a sample database of addresses, checking that the software correctly identifies deliverable addresses, adds ZIP+4 codes, assigns carrier route information, and standardizes address formatting. Systems must score at least 98.5% in some categories (such as ZIP+4 and carrier route) and 100% in others (such as delivery point coding and DPV) to pass, and certification must be earned again for each two-year certification period.
CASS-certified software provides critical data elements beyond basic address validation. It returns ZIP+4 codes that specify delivery areas down to a city block or building, carrier route codes that identify the specific mail delivery route, delivery point barcodes for automated sorting, and DPV (Delivery Point Validation) codes that confirm whether an address is deliverable. This enriched data enables the USPS to sort mail more efficiently and is required for mailings claimed at automation prices.
For businesses, using CASS-certified address verification is essential for several reasons. First, accurate coding helps cut mail that cannot be delivered as addressed. Second, CASS-certified coding is required to claim automation prices. Third, it meets the USPS addressing rules for those mailings. Fourth, it improves overall data quality by maintaining clean, standardized customer addresses.
The cost effect depends on the mailing. CASS certification alone is not a discount: a mailing earns a lower price only when it meets every standard for that price, and the size of any saving depends on the price the mailing claims. Fewer returned pieces also mean less spent on reprinting and resending.
How CASS Certification Works
- Vendor Application: Software provider applies to USPS for CASS certification and receives test database
- System Testing: Provider processes test addresses through their verification system, generating standardized output
- Accuracy Evaluation: USPS evaluates results against known correct values, measuring accuracy across multiple criteria
- Certification Issuance: If the software meets the minimum score in every required category (98.5% or 100%, depending on the category), USPS grants CASS certification
- Database Updates: Certified provider receives monthly USPS database updates to maintain current address data
- Renewal Every Two Years: Certification is valid until the end of the current two-year certification period and must be earned again through retesting
Key Benefits of CASS Certification
Postage Discounts
CASS-certified coding is required to claim automation prices on bulk mailings
Reduce Undeliverable Mail
Cut mail that cannot be delivered as addressed through accurate address coding and standardization
USPS Compliance
Meet postal regulations and requirements for bulk mailing and presort operations
Faster Delivery
Improve mail delivery speed through accurate sorting codes and carrier route information
Data Quality
Maintain clean, standardized customer address database in the postal standard format
Cost Savings
Fewer returned pieces mean less spent on reprinting and resending; any postage saving depends on the price the mailing claims
Common Use Cases
1. Direct Mail Marketing
Process marketing mailings with CASS-certified addresses to claim automation prices and cut undeliverable mail
2. E-commerce Shipping
Verify customer shipping addresses with CASS certification to reduce failed deliveries and improve customer satisfaction
3. Billing & Statements
Ensure bills and financial statements reach customers reliably by using CASS-verified addresses for mailings
4. Magazine & Subscription Services
Maintain accurate subscriber addresses and qualify for periodical mailing discounts through CASS certification
5. CRM Database Cleansing
Clean and standardize customer databases using CASS-certified verification to improve data quality and deliverability
CASS Certification vs Standard Address Validation
| Feature | Standard Validation | CASS Certified |
|---|---|---|
| USPS Certification | No official certification | Officially certified by USPS |
| Accuracy Requirement | No postal test score | 98.5% or 100%, by test category |
| 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 |
| Presort Eligibility | Cannot be used to claim automation prices | Required to claim automation prices |
| Cost | Lower | Higher |
| Best For | Basic address checking | Bulk mailing, compliance, savings |
How to Implement Address Verification with sthan.io
sthan.io provides address verification that standardizes addresses to the postal 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's address verification:
Step 1: Get API Credentials
Sign up for free at sthan.io and get your API credentials from the dashboard
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Step 2: Make API Request
GET https://api.sthan.io/v2/address-verification/usa/speculative/1600 Amphitheatre Parkway, Mountain View, CA 94043 Authorization: Bearer YOUR_TOKEN
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