NetSuite has no control over the address validation. NetSuite strictly utilizes the FedEx or UPS address verification API when the integrated shipping is used. This API provides a check of verification of the address inputted by the user by sending the data into the FedEx or UPS system. FedEx or UPS verifies if this address is confirmed or not.
Users have the option to turn off this verification at a per account basis. There is no option to turn off any partial pieces of the functionality.
If you want to check the address on internet, please use the link provided by the error message (http://zip4.usps.com/zip4/welcome.jsp).