Flat-Size Mail

A mailpiece that exceeds one of the dimensions for letter-size mail (11-1//2 inches long, 6-1/8 inches high, and ¼ inch thick), but does not exceed the maximum dimension for this mail processing category (15 inches long, 12 inches high, and 3/4 inch thick). The dimensions are slightly different for automation rate eligibility. It may be unwrapped, paper-wrapped, sleeve wrapped, or enveloped.