What code must all pieces in an automation flat-size mailing contain?

In automation flat-size mailings, the Intelligent Mail Barcode is essential. This specific barcode allows for the efficient processing and tracking of mail by the postal service. It encodes multiple pieces of information, including the destination address, unique identifiers for the mail piece, and other relevant data that supports automated sorting and delivery. By using the Intelligent Mail Barcode, mailings benefit from improved tracing capabilities, reduced handling time, and more accurate delivery services.

The other options do not fulfill the necessary requirements for automation flat-size mailings. QR Codes are primarily used for quick access to information but do not serve the same tracking or sorting purposes. Freight Charge Codes relate to shipping costs rather than mailing automation, while Service Codes are not specifically required in the context of automation mail preparation. The use of the Intelligent Mail Barcode is a standardized practice aimed at enhancing operational efficiency within postal services.