ACS is a post mailing service that allows mailers to receive change-of-address (COA) and other reasons for non-delivery electronically and reduce the number of manual (hardcopy) address notifications.

Traditional ACS is one of the four ways to participate in ACS, where mailers receive notifications of undeliverable mail (UAA) and change-of-address (COA) electronically. The Intelligent Mail^® barcode is not required to receive Traditional ACS.

OneCode ACS allows customers mailing First-Class Mail^®, Standard Mail^®, and Periodical flats or letters to receive electronic or automated address corrections using the Intelligent Mail^® barcode.