Retail Priority Mail Express postage may be paid with adhesive stamps (see 604.1.0) or with meter stamps (see 604.4.0).The mailer is responsible for proper payment of postage.
In a postage-affixed Priority Mail Express mailing, the mailer must affix to each piece a value in adhesive stamps or meter stamps equal to at least the postage required.
Meter stamps may be used to prepay reply postage on any Priority Mail Express shipment. The mailer must place meter stamps, sufficient to prepay postage in full, on the envelope, tube, or other mailing container that bears the return address of the meter license holder. Reply mail prepaid with meter stamps is delivered only to the address of the meter license holder. If the address is altered, the mail is held for postage.