Delivery information is only as good as the quality of the address data. Our goal is to help customers send their mail to the correct address every time. To help meet this objective, ACS is designed to substantially reduce the number of manual address correction notifications sent to mailers and replace them with electronic notices.

ACS has four distinct implementation methods: Traditional ACS, using a USPS-assigned Participant Code and optional keyline; OneCode ACS or Full Service ACS, using the Intelligent Mail barcode; and IMpb ACS, using the Intelligent Mail package barcode. Each method offers several different options. There is also a special subset of ACS called Shipper Paid Forwarding/Return, which may be used for heavy catalogs and parcels. Technical information on all ACS services is available at — scroll down to the section titled “ACS Technical Guides.” Technical information on how to qualify for Full Service ACS is available at

To participate in ACS, mailers must modify their mailing label and/or mailpiece. The type of modification needed depends on the type of ACS implementation method chosen. Clarification regarding the required modifications is available in the Publication under the sections entitled “Traditional ACS,” “OneCode ACS,” “IMpb ACS,” and “Full Service ACS.”

Once an ACS-modified mailpiece is identified as undeliverable as addressed (UAA) and processed in the USPS nationwide network of Postal Automated Redirection System (PARS) and Computerized Forwarding System (CFS) sites, an electronic COA or nixie notice is generated. Mailers are advised that ACS is an enhancement to the original manual (hard copy) notices provided by Post Offices. It does not completely replace or eliminate hard copy address change notifications.