Address Change Notification
For presorted first-class mail, the post office requires that the addresses you use are correct through CASS certification, and that the person to whom you address the mailing resides at that address. The United States Postal Service® offers, for a fee, the Address Change Service (ACS). As a participant, you're notified if an addressee moves, and the new address is sent to you.
To use the service, you must obtain a participation code and print the phrases "Address Service Requested" or "Change Service Requested" on mailings. View other details of participation.