CASS is a United States Postal Service (USPS) acronym that stands for Coding Accuracy Support System. The term CASS is widely used by the USPS when they refer to the verification status of an address list. In order for an address list to receive CASS certification, the list must be checked against the USPS Address Matching System (AMS) CD-ROM, a match must be found for each address and the correct 11-digit Delivery Point ZIP code and corresponding barcode must be added. Only addresses with the Delivery Point ZIP code and barcode are eligible for automation bulk mailing rates. A mailing list must undergo address verification every six months (every three months for Carrier Route mailings) and is particularly important to mailers because of the difference between "automation" and "non-automation" mailing rates, which is about five cents per piece. For a 10,000-piece mailing, CASS certification of the address list could save the mailer approximately $500.

The AMS is maintained by the USPS and provides information on every address in the United States – over 140 million addresses. Mailers must use a software package that is CASS-certified by the USPS to perform address verification. Similar to tax software, users must update their software annually to maintain the certification status. When a bulk mailing is submitted, a PS 3553 report (also known as a CASS Certificate) must accompany it to substantiate that the address list has been checked using the Address Matching System and meets all USPS specifications. All Envelope Manager Software products are CASS-certified and will print the PS 3553 report for mailings. Envelope Manager provides two methods for CASS certification: