49 C.F.R. § 1111.4
A complainant is responsible for serving formal complaints, amended or supplemental complaints, and cross complaints on the defendant(s). Service shall be made by sending a copy of such complaint to the chief legal officer of each defendant by either confirmed facsimile and first-class mail or express overnight courier. The cover page of each such facsimile and the front of each such first-class mail or overnight express courier envelope shall include the following legend: "Service of STB Complaint". Service of the complaint shall be deemed completed on the date on which the complaint is served by confirmed facsimile or, if service is made by express overnight courier, on the date such complaint is actually received by the defendant. When the complaint involves more than one defendant, service of the complaint shall be deemed completed on the date on which all defendants have been served. The complaint should be filed with the Board together with an acknowledgment of service by the persons served or proof of service in the form of a statement of the date and manner of service, of the names of the persons served, and of the addresses to which the papers were mailed or at which they were delivered, certified by the person who made service.
49 C.F.R. §1111.4