3 Basics

3-1 Minimum Requirements for All Mail

All mail must meet minimum size standards to be mailable. Mailpieces that are 1/4 inch thick or less must be rectangular in shape with four square corners and parallel opposite sides and at least 3–1/2 inches high, 5 inches long, and 0.007 of an inch in thickness.

Mailpieces that do not meet the minimum size standards are nonmailable.