Can tape be used to close, reinforce or enlarge Priority Mail service Flat Rate envelopes / boxes?
When mailing using the Priority MailĀ® service, Express MailĀ® service or Priority Mail InternationalĀ® flat rate, the contents of the Flat Rate envelope must be confined within the envelope with the adhesive provided on the flap as the primary means of closure. Contents must also be confined within the box secured with tape.