All mail that weighs over 13 ounces and that uses only postage stamps as postage (this includes pre-paid Priority Mail Flat-Rate Boxes and Envelopes) must be presented to an employee at a retail service counter at a Post Office. This is part of ongoing security measures established by the Postal Service, in cooperation with other government agencies, to keep the public, customers, employees, and the mail safe.
Customers may use a convenient online postage application or generate postage on an Automated Postal Center® (APC®) if they wish to mail items that weigh more than 13 ounces. Online postage applications include the Postal Service’s Click-N-Ship service available at www.usps.com and PC Postage from an authorized USPS postage vendor. Customers may deposit items with online and electronic postage in Postal Service collection boxes or Post Office lobby mail slots, or give them to their USPS letter carrier. Alternate places customers can mail items are at contract postal units and USPS Approved Shipper locations.
Customers who are unable to use one of the above methods to prepare and affix postage must present items weighing more than 13 ounces to a Postal Service employee at a Post Office retail service counter. Business customers who use postage meters may continue to use meter postage for packages of any weight and mailing method.