list based on the standardized address Qualify for USPS bulk mailing discounts Minimize delivery delays by only using valid addresses Providers The USPS offers address verification directly on their website. Addresses are processed one at a time by typing the address into the provided fields. The USPS also licenses their services to third-party companies that provide the CASS certification in bulk. These third-party providers typically allow processing of address lists in CSV or Excel format. They may also provide an API allowing the use of address verification services from within a program or website. In the UK, the Royal Mail provides address verification directly on their site and also licence their data to third-party providers to allow address checking services to be provided to organizations wishing to capture accurate addresses in their ecommerce checkout and online forms. References Postal systems