Can you put tape on USPS Priority Flat Rate Envelopes and/or Boxes?

MailProNews for Mailing Professionals


When sealing a Priority Mail Flat Rate Box — or flat-rate envelope — the container flaps must be able to close within the normal folds. Mailers can apply any amount of tape to the flaps and seams for closure or to reinforce the container, provided the design of the container is not enlarged by opening the sides, and the container is not reconstructed in any way. As long as it closes properly, a flat-rate envelope or box can contain oddshaped items.

via MailPro – Vol. 3 Number 3 May/June 2009.