A summons may be served on a person outside this state in any manner provided by this article or by sending a copy of the summons and of the complaint to the person to be served by first-class mail, postage prepaid, requiring a return receipt. Service of a summons by this form of mail is deemed complete on the 10th day after such mailing.
Source:
Section 415.40, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CCP§ionNum=415.40..