39 C.F.R. § 265.8
(a) Requirements for making an appeal. Requesters may appeal adverse decisions rendered by the Postal Inspection Service or any Postal Service component by mail to the General Counsel, U.S. Postal Service, 475 L'Enfant Plaza SW., Washington, DC 20260; or by email to foiaappeal@usps.gov. The requester must make the appeal in writing and to be considered timely it must be postmarked, or in the case of electronic submissions, transmitted, within 90 calendar days after the date of the response; or within a reasonable time if the appeal is from a failure of the custodian to act. The General Counsel may, in his or her discretion, consider late appeals. In the event of the denial of a request or of other action or failure to act on the part of a custodian from which no appeal is taken, the General Counsel may, if he or she considers that there is doubt as to the correctness of the custodian's action or failure to act, review the action or failure to act as though an appeal pursuant to this section had been taken. A letter of appeal should include, as applicable:
(b) Adjudication of appeals.