If your US based business maintains customer's physical addresses and it is important to keep your data current, the USPS provides NCOA, National Change of Address, data to various providers you can subscribe to.
J. Q. Public fills out the form at the post office that they're moving from 100 Main St Anytown to 200 Elm Ln Othertown you'll get an update in the next month's data release and you can update your records (and mail has already been forwarded).