D.C. Mun. Regs. tit. 17, § 2413
2413.1 Any notice required by § 2410 or § 2412 may be served either personally by a member of the Board or by certified mail, return receipt requested, directed to the person concerned at his last known residence or business address as shown by the records.
2413.2 If notice is served personally, it shall be deemed to have been served at the time when delivery is made to the person concerned.
2413.3 If notice is served by certified mail, it shall be deemed to have been served on the date borne upon the return receipt showing delivery of the notice to the person concerned or refusal of the person concerned to receive notice.
2413.4 If the person concerned is no longer at the last known address as shown by the records and no forwarding address is available, the notice shall be deemed to have been served on the date the return receipt bearing such notification is received by the Board.
SOURCE: § 22.2 of Regulation No. 73-13, approved May 24, 1973, 19 DCR 1147, 1150 (June 11, 1973), 25 DCRR § 22.2.