CASS stands for Coding Accuracy Support System. This certification is given to an address once it is verified as deliverable (address standardization must occur first). Once an address is CAAS certified, mailers can be sure that the zip code, carrier route, and 5-digit coding are correct. The USPS assigns delivery point codes to specific mailboxes, which are also checked through the CASS certification process. By catching these and other errors, such as typos, mailers can ensure their mailing list is clean and accurate before each campaign goes out.