For an address to be validated it has to match the address in the United States Postal Service's address database.
If an address contains any incorrect information, it will not match a corresponding address in that database, and therefore show as "invalid". The easiest way to double check the address is to do a quick search on the USPS address database by clicking here. Then just follow the steps listed below.
Step 1: Enter the information that you have on the address
Step 2: Verify the Information Entered Matches the official USPS Address
IMPORTANT NOTE: Sometimes an address will not validate because the address is marked as "vacant" by the USPS. New addresses, unregistered addresses, or addresses located within a postal code primarily serviced by PO boxes, would all fail to validate.