Idaho Rules of Civil Procedure Rule 4(e)(1). Summons - Other Service.
Whenever a statute of this state provides for service of a summons, or of a notice, or of an order in lieu of summons, upon a party not an inhabitant of, or found within the state, or upon unknown persons, service shall be made under the circumstances and in the manner prescribed by the statute. Personal service outside of the state, when authorized by statute, shall be as provided by Rule 4(d). Whenever the summons, notice or order is served by publication it shall contain in general terms a statement of the nature of the grounds of the claim, and copies of the summons and complaint shall be mailed to the last known address most likely to give notice to the party.