45 C.F.R. § 501.3 – Service of process.

(a) By whom served. The Commission will serve all orders, notices and other papers issued by it, together with any other papers which it is required by law to serve.
(b) Kinds of service. Subpoenas, orders, rulings, and other processes of the Commission may be served by delivering in person, by registered or certified mail, by overnight express delivery service, by first class mail, by telegraph, or by publication.
(c) Personal service. Service by delivering in person may be accomplished by:
1. (1) Delivering a copy of the document to the person to be served, to a member of the partnership to be served, to an executive officer or a director of the corporation to be served, or to a person competent to accept service; or
2. (2) By leaving a copy thereof at the residence, principal office or place of business of the person, partnership, or corporation.
3. (3) Proof of service. The return receipt for the order, other process or supporting papers, or the verification by the person serving, setting forth the manner of service, will be proof of the service of the document.
4. (4) Service upon attorney or agent. When any party has appeared by an authorized attorney or agent, service upon the party's attorney or agent will be deemed service upon the party.
(d) Service by registered mail or certified mail. Service by registered mail or certified mail will be regarded as complete on the date the return post office receipt for the orders, notices and other papers is received by the Commission.
(e) Service by overnight express delivery service or by first class mail. Service by overnight express delivery service or first class mail will be regarded as complete upon deposit, respectively, in the delivery service's package receptacle or in the United States mail properly stamped and addressed.
(f) Service by telegraph. Service by telegraph will be regarded as complete when deposited with a telegraph company properly addressed and with charges prepaid.
(g) Service by publication. Service by publication is completed when due notice has been given in the publication for the time and in the manner provided by law or rule.
(h) Date of service. The date of service is the day upon which the document is deposited in the United States mail or delivered in person, as the case may be.
(i) Filing with Commission. Papers required to be filed with the Commission will be deemed filed upon actual receipt by the Commission accompanied by proof of service upon parties required to be served. Upon the actual receipt, the filing will be deemed complete as of the date of deposit in the mail or with the telegraph company as provided in paragraphs (e) and (f) of this section.