If an Action is rejecting a supporter's address, then the first step you should take for investigation is to hop on over to the USPS Address Lookup site.
There, enter the supporter's address, exactly as they entered it into the Action. Our address validation goes directly against the USPS data. Some legislators also use USPS data to verify that the supporter is in district as well. If USPS doesn't recognize the address, as entered, then our system will not either.