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The CASS™ certification process is designed in cooperation with the mailing industry to improve the accuracy of postal codes, i.e., Five-Digit ZIP Code®, ZIP + 4®, delivery point (DPCs), and carrier route codes that appear on mailpieces. 

Who is CASS™ for?

CASS™ certification is available to all software developers, mailers, and service bureaus who wish to evaluate the quality of their address matching software. Any mailing claimed at an automation price must be produced from address lists properly matched and coded with CASS-certified address matching methods.

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What is CASS™?

The CASS™ software certification program provides hardware and software developers, service bureaus, and commercial mailers a common measure by which to test the quality of address-matching software. Software tests for CASS™ certification are graded by the U.S. Postal Service®, National Customer Support Center (NCSC) and the results are returned to the developer to provide useful diagnostics for correcting software deficiencies. However, CASS™ processing does not measure the accuracy of ZIP + 4, delivery point, Five-Digit ZIP Code, or carrier route codes in a mailer’s address file.

CASS™ enables the Postal Service™ to evaluate the accuracy of address matching software programs in the following areas.

  • 5-digit coding
  • ZIP + 4/ delivery point (DP) coding
  • Carrier route coding
  • DPV® or DSF
  • LACSLink®
  • SuiteLink®
  • eLOT®
  • RDI™

CASS™ allows developers, vendors and mailers the opportunity to test their address matching software packages and after achieving a specified percentage of compliance to be certified by the Postal Service. CASS™ enables mailers to measure and diagnose internally written, commercially available address matching software packages. The effectiveness of service bureaus' matching software can also be measured.

How does CASS work?

There are two stages in the CASS process:

Stage 1: CASS Test WIth Answers (optional)

The CASS™ Stage I file is a self-test that helps developers measure and diagnose the performance of their address-matching software when it is applied to a CASS™ test address file. The Stage I results assist developers with software debugging and troubleshooting in preparation for Stage II of the CASS™ certification process. The Stage I file contains approximately 150,000 test addresses extracted from the City State and ZIP + 4 files with samples of all types of addressing used around the country. Some test addresses have been changed for test purposes, and not all records have valid ZIP + 4 codes or valid addresses.

Customers can evaluate the accuracy of their address-matching software by applying the correct carrier route, Five-Digit ZIP, ZIP + 4 codes, DPV or DSF2, LACSLink and SuiteLink elements and by comparing the applied codes with the correct codes provided by the Postal Service. The results of Stage I processing are not reviewed by the NCSC and have no effect on CASS certification. 

Stage 2: CASS Test Without Answers (required for certification)

CASS™ Stage II files are used to test the address matching software performance by processing a test address file that is returned for evaluation by the CASS™ Department. The CASS™ Stage II file contains approximately 150,000 test addresses that are extracted and presented in the same makeup and mixture as Stage I without answers.Customers use their address-matching software to apply the correct data applicable to the test record.

Match rates using CASS™ Certified software vary greatly depending on address hygiene, the quality of addresses used, and the timeliness of the customer database update applications. An address with an incorrect Five-Digit ZIP Code, ZIP + 4 code, carrier route code, ZIP + 4 or an address with no ZIP + 4 code or failure to process using DPV or DSF2, LACSLink and SuiteLink elements can contribute to delays in processing mail.

To achieve CASS™ certification, participants must pass with a minimum score of 98.5 percent for ZIP + 4, carrier route, Five-Digit ZIP and LACSLink, 100 percent for delivery point coding, eLOT, DPV or DSF2, RDI and Perfect Address. CASS™ certification is valid until the end of the current certification period. To remain CASS™ certified for each required certification period, developers must reapply for certification and meet the minimum accuracy requirements during Stage II testing.

Maintaining Certification

CASS™ certification is valid until the end of the current biennial period. For software to remain CASS™ Certified for each biennial period, developers must reapply for certification and meet the minimum accuracy requirements during Stage II testing.

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Featured Resources

CASS™ Cycle O

CASS™ Cycle N 2011-2020

Related Products


The MASS™ certification is an extension of the CASS™ system, which is a process designed in cooperation with the mailing industry to improve the accuracy of postal codes that appear on mail.

ZIP + 4® Product

The ZIP + 4® Product is a base reference file that can be accessed by an application to assign the correct ZIP + 4® Code associated with a physical address.


Business or residential? Make informed decisions, improve your deliverability, and optimize operational efficiency with RDI™. 


The LACSLink® product offers an automated method of obtaining new addresses after a 911 emergency system has been implemented.


The SuiteLink® product enables customers to provide improved business addressing information by adding known secondary (suite) information to business addresses, which will allow USPS delivery sequencing where it would not otherwise be possible.

Enhanced Line of Travel (eLOT®)

The eLOT product allows mailers the ability to sort their mailings in approximate carrier-casing sequence.

Carrier Route Product

The Carrier Route Product provides reference information needed to apply carrier route codes to addresses for presort postage discounts.


For more information about the CASS™ certification process, contact us at 800-238-3150 or email

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