"Domestic Mail Manual (DMM)"
The Domestic Mail Manual is the USPS manual that contains the basic standards governing U.S. domestic mail services, descriptions of the mail classes and special services and conditions governing their uses, and standards for rate eligibility and mail preparation. Domestic mail is classified by size, weight, content, service, and other factors.
Offsite Links
An online version of the DMM can be found on the USPS web site.