14 CFR § 1264.125 - Form, filing, and service of papers.
(1) Documents filed with the presiding officer shall include an original and two copies.
(2) Every pleading and paper filed in the proceeding shall contain a caption setting forth the title of the action, the case number assigned by the presiding officer, and a designation of the paper (e.g., motion to quash subpoena).
(4) Papers are considered filed when they are mailed. Date of mailing may be established by a certificate from the party or its representative or by proof that the document was sent by certified or registered mail.
(b) Service. A party filing a document with the presiding officer shall, at the time of filing, serve a copy of such document on every other party. Service upon any party of any document other than those required to be served as prescribed in § 1264.107 shall be made by delivering a copy or by placing a copy of the document in the U.S. mail, postage prepaid, and addressed to the party's last known address. When a party is represented by a representative, service shall be made upon such representative.
(c) Proof of service. A certificate of the individual serving the document by personal delivery or by mail, setting forth the manner of service, shall be proof of service.