Which of the following is true regarding the flexibility standards for flats eligible for mailing at an automation price?

The statement that flats must be flexible and not droop aligns with the requirements for mailing at an automation price. Flexibility in this context means that while the mail piece should be able to bend slightly, it should not lose its shape or droop excessively. This characteristic is important because automation equipment, which processes these flats, relies on consistent and predictable mail piece dimensions for efficient sorting and handling.

If a mail piece droops or lacks sufficient flexibility, it could lead to problems during processing, such as jams in sorting machines or incorrect reading by barcode scanners. Therefore, complying with the flexibility standards ensures that mail is processed smoothly and efficiently, allowing it to qualify for reduced automation prices.

The other options address aspects that are not directly related to the flexibility standard required for automation pricing. Rigid and unyielding mail pieces would not be compliant; weight and volume limits pertain to overall physical characteristics but do not specify about flexibility.