What is Priority Mail Express® and how does it relate to patent filings?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

Priority Mail Express® is a service offered by the United States Postal Service (USPS) that can be used to establish a filing date for patent applications and other correspondence with the USPTO. As stated in MPEP 513:

The statutory authority for the granting of a filing date based on the date of deposit for correspondence sent by Priority Mail Express® and received by the Office is found in section 21(a) of Title 35 of the United States Code.

Using Priority Mail Express® allows applicants to receive a filing date as of the date the correspondence was deposited with USPS, rather than the date it was received by the USPTO.