Idaho Code § 55-1821: Service of process.

In addition to the methods of service provided for in the Idaho rules of civil procedure and Idaho statutes, service may be made on a person who has filed a consent to service of process by delivering a copy of the process to the office of the commission, but it is not effective unless the plaintiff (which may be the commission in a proceeding instituted by it):

(1) Forthwith sends a copy of the process and of the pleading by certified or registered mail to the defendant or respondent at his last known address; and

(2) The plaintiff’s affidavit of compliance with this section is filed in the case on or before the return day of the process, if any or within such further time as the court allows.