The USPS and Mailing Standards G020 Mailing Standards Summary G020 describes the Domestic Mail Manual. It also a covers a mailer's responsibility to comply with all postal standards and the procedures for appealing a classification decision.
Domestic mail is classified by size, weight, content, service, and other factors.
1.2 Terms Terms in the DMM referring to only one sex apply to persons of either sex. Terms referring to the singular also apply to the plural, unless the context indicates otherwise. A copy is also filed at the Office of the Federal Register, National Archives and Records Administration. 1.4 Revisions The USPS reserves the right to change the standards in the Domestic Mail Manual. Substantive revisions are published in the Postal Bulletin and, when appropriate, the Federal Register.