(1) All notices, pleadings, and other papers filed with the hearing officer shall be served upon all counsel and representatives of record and upon unrepresented parties or upon their agents designated by them or by law.

(2) Service shall be made personally or, unless otherwise provided by law, by first-class, registered, or certified mail; or by commercial parcel delivery company.

(3) Service by mail shall be regarded as completed upon deposit in the United States mail properly stamped and addressed. Service by commercial parcel delivery shall be regarded as completed upon delivery to the parcel delivery company, properly addressed with charges prepaid.

(4) Proof of service. Where proof of service is required by statute or rule, filing the papers with the hearing officer, together with one of the following, shall constitute proof of service:

(a) An acknowledgment of service.

(b) A certificate that the person signing the certificate served the papers upon all parties of record in the proceeding by delivering a copy thereof in person to (names).

(c) A certificate that the person signing the certificate served the papers upon all parties of record in the proceeding by:

(i) Mailing a copy thereof, properly addressed with postage prepaid, to each party to the proceeding or his or her attorney or authorized agent; or

(ii) Depositing a copy thereof, properly addressed with charges prepaid, with a commercial parcel delivery company.