49 CFR §209.5

1. (a)Each order, notice, or other document required to be served under ch. II of subtitle B of title 49 of the Code of Federal Regulations must be served by the following method:
   1. (1)Any electronic method of delivery so long as there was no indication received that any transmission had failed; or
   2. (2)In the event an electronic method of delivery is impossible, service may be made by U.S. mail.
2. (b)Service upon a person's duly authorized representative constitutes service upon that person.
3. (c)The date of service will be:
   1. (1)If sent by an electronic method of delivery, the date of electronic transmission to the party to be served.
   2. (2)In the event an electronic method of delivery is impossible, and mailing is used, the postmark date. An official U.S. Postal Service receipt from a registered or certified mailing constitutes prima facie evidence of service.
4. (d)Each pleading must be accompanied by a certificate of service specifying how and when service was made.
5. (e)When service must occur within a particular timeframe, the date certain when service must be completed will be determined in accordance with the computation of time provisions in Rule 6 of the Federal Rules of Civil Procedure, as amended.