A summons may be served on an artificial person (other than a natural person) by leaving a copy of the summons and complaint in the office of the person to be served, during usual office hours, with the person who is apparently in charge thereof, and by thereafter mailing a copy of the summons and of the complaint (by first-class mail, postage prepaid) to the person to be served at the place where a copy of the summons and of the complaint were left. Or, the summons and complaint may be served by substitution at the defendant’s usual mailing address, other than a United States Postal post office box , if no physical address is known. Service of a summons in this manner is deemed complete on the 10th day after such mailing. (CCP 415.20(a))
Judicial Council Comment: “The papers must be delivered to a person who is apparently in charge of such office, such as the personal secretary of the person to be served, and such delivery must be made during usual office hours.” Due diligence is not required for substitute service on an artificial person.