The notice required by section 6-320(d), Idaho Code, shall be served either:
(1) By delivering a copy to the landlord or his agent personally; or
(2) If the landlord or his agent is absent from his usual place of business, by leaving a copy with an employee at the usual place of business of the landlord or his agent; or
(3) By sending a copy of the notice to the landlord or his agent by United States Postal Service certified mail, return receipt requested.