Postal address verification (also known as address , address validation, address verification and CASS certification) is the process used to check the validity and deliverability of a physical mailing address. According to the United States Postal Service, an address is valid (or mailable) if it is CASS-certified, meaning that it exists within the comprehensive list of mailable addresses in their Address Management System. This is different from the credit card Address Verification System (AVS), which is the method used by credit card processors to authenticate ownership of a credit card by verifying that the account on the credit card matches the billing address on file. Credit card AVS does not determine deliverability of an address. Standardization Before an address can be certified as deliverable (CASS-certified), it must first be standardized. Standardization converts an address into a standard format by correcting the address, if possible, and adding missing information, such as a ZIP code, to produce a complete address containing a street address, city, state, and ZIP code. The following methods are used to achieve the most accurate address possible: Abbreviation USPS approved abbreviations are used whenever possible to clarify and shorten the address. Example: The term avenue may commonly be abbreviated AV, AVEN, or AVN or fully spelled out as avenue. The standardized form is AVE. Similarly, Square is commonly abbreviated SQRE, SQR, or SQU, while the standardized form is "SQ". Spelling correction Because a misspelling usually results in an undeliverable address, commonly misspelled words are corrected. These are typically city names and street names. Due to the large number of possible misspellings, not all of them can be accurately detected and corrected. Example: The street address 1600 parkways is corrected to 1600 Amphitheatre PKWY. The spelling of the city name as "" is corrected to "Phoenix". Uniform city names Many cities have several different, commonly used names. Each ZIP Code in the Address Management System has one preferred city name and may have one or more acceptable city names. CASS-certified software accepts as standard any "preferred" or "acceptable" city for a five-digit ZIP Code. Only a city that is "preferred" or "acceptable" is recognized as standard. These systems attempt to correct incorrect city names and any that cannot be corrected are rejected. Examples: "New York City", "Empire State", "Greeley Square" and "Manhattan" in ZIP Code 10001 is standardized to "New York". Meanwhile, the "preferred" city of "Floral Park" or