Which option requires mailers to apply unique Intelligent Mail barcodes on mailpieces?

The Full-Service Option is the correct choice because it mandates that mailers use unique Intelligent Mail barcodes on each mailpiece. This requirement is in place to enhance tracking and visibility throughout the mailing process, allowing for better management of mail campaigns and more accurate data reporting.

The implementation of unique barcodes per mailpiece unlocks additional features, such as providing advanced insights about mail delivery, assuring that pieces are tracked individually from acceptance to delivery. In contrast, other options like Standard Mail or Basic Mail may not require such specific tracking measures, offering less comprehensive services and reporting features to mailers. The Express Mail Option, while focusing on expedited delivery, does not carry the same requirements for unique barcoding at the piece level as stipulated by the Full-Service Option.