Mailers may use staples or steel stitching to close boxes as follows: For easy loads of up to 5 pounds, paper bags and wraps are acceptable when at least of a 50-pound basis weight (the strength of an average large grocery bag) and the items are immune from impact or pressure damage.
When using hot-melt adhesive, apply adhesive using one of these methods: When banding is used for closure and reinforcement, it must encircle the length and girth of the package at least once.
See the physical standards for processing categories in The placement of the address on a letter-size mailpiece may render a piece nonmailable or nonmachinable.
If the length (the dimension parallel to the address) of a letter-size mailpiece is not at least 5 inches, it is nonmailable.
If the height (the dimension perpendicular to the length) of a letter-size mailpiece is not at least 3-1/2 inches, it is nonmailable.
If the aspect ratio (length divided by height) is not within 1.3 to 2.5 (inclusive), the piece is a nonmachinable letter.