24 C.F.R. § 2004.10 Service of an Office of Inspector General subpoena.
Service of a subpoena issued by OIG may be accomplished as follows:
(a) Personal service. Service may be made by delivering the subpoena to the person to whom it is addressed. If the subpoena is addressed to a corporation or other business entity, it may be served upon an employee of the corporation or entity. Service made to an employee, agent, or legal representative of the addressee shall constitute service upon the addressee.
(b) Service by mail. Service may also be made by mailing the subpoena, certified mail—return receipt requested, to the addressee at his or her last known business or personal address.