The United States Postal Service (USPS) rates are based on mail that is automation compatible.
Machinable: mail pieces that fall within the min/max size specs, rectangular in shape, constructed of paper and sealed per USPS specifications. Charged at a lower rate.
Non-machinable: mail pieces that include rolls, tubes, and anything irregularly shaped, which do not comply with the size and aspect ration requirement and thus cannot be sorted on automated equipment. Charged at a higher rate.
Always show a folded mock-up to your post office agent to ensure it meets the USPS guidelines prior to finalizing your design. The standards and requirements listed are current at ...