D.C. Mun. Regs. tit. 16, r. 16-1506
Each paper required to be filed with the Office of Adjudication shall be served on all parties by the party filing the papers.
If a party has retained an attorney as provided in §§ 1520.1 and 1520.2, all papers except the petition (§ 1509) and subpoena (§ 1507) shall be served on that attorney in place of the party.
The Director shall serve petitions or subpoenas in the manner set forth in the Superior Court for the District of Columbia Rules of Civil Procedure for personal service (Rule 4(d)).
Service of papers other than the petition or subpoenas may be made in accordance with § 1506.3 or by delivering a copy to the party or by mailing it to the party at his or her last known address.
Service of papers other than subpoenas or petitions shall be considered complete when mailed postage prepaid U.S. first-class mail.
Proof of service of each document filed with the Office of Adjudication, stating the name and address of the person served and the manner and date of service, shall be filed with the Office of Adjudication, and may be made by any of the following methods:
Appearance at the hearing by a party served with a petition shall establish proper service of the petition, unless the appearance is solely for the purpose of arguing the issue of the validity of service.
D.C. Mun. Regs. tit. 16, r. 16-1506