39 C.F.R. § 3010.127 – Service.

(a) Material filed by a person participating in a docket shall be deemed served on all other persons (except those served by the Secretary pursuant to paragraph (b) of this section) who are participating in the docket as of the date the material, or notice of the material's filing is posted by the Secretary on the Commission's website.
(b) The Secretary shall provide service by First-Class Mail, which is deemed complete upon mailing, to the following persons upon a demonstration of the inability to effectively utilize the Filing Online system (until alternative arrangements are established):
1. (1) Petitioners in dockets appealing Postal Service determinations to close or consolidate post offices conducted pursuant to part 3021 of this chapter;
2. (2) Parties that have intervened in proceedings docketed for a hearing on the record; and
3. (3) Where necessary for fairness and protection of due process, an active participant in a proceeding affecting the substantial rights of that participant.
(c) The Secretary shall maintain a current service list in each proceeding docketed for a hearing on the record which shall include the parties that have intervened in that proceeding and up to two individuals designated for physical service of documents, if necessary, by each party. The service list for each current proceeding will be available on the Commission's website at http://www.prc.gov. Each party who has internet access shall be responsible for ensuring that its listing on the Commission's website is accurate and should promptly notify the Secretary of any errors. The Secretary or the Secretary's designee shall be responsible for ensuring the accuracy of listings of any parties who lack internet access.