All items that may be sent as First-Class Mail International (see 241) may be sent in the Priority Mail International flat-rate envelope provided that the contents are mailable, that they fit securely in the envelope, and that they are entirely confined within the envelope with the provided adhesive as the means of closure. The envelope flap must be able to close within the prefabricated folds. Tape may be applied to the flap and seams for closure or to reinforce the envelope, provided the design of the envelope is not enlarged by opening the sides of the envelope and taping or reconstructing the envelope in any way. Registered Mail service is available. Insurance is not available.