Priority Mail postage may be paid with postage stamps (see 604.1.0), or meter stamps (see 604.4.0).
In a postage-affixed mailing, the mailer must apply enough value in adhesive stamps or meter stamps equal to the postage required (including any surcharges). A mailer also may use precanceled stamps on Priority Mail.
Priority Mail Forever Prepaid Flat Rate packaging must be purchased by credit card online at www.usps.com and bears a shipping label with affixed Forever Prepaid postage. Mailers adding extra services must take packages to a retail Post Office location for payment of the associated fees for each extra service added. USPS Tracking (electronic option) is included at no additional cost.