California Code, Code of Civil Procedure - CCP § 1020

(a) Any notice required by law, other than those required to be given to a party to an action or to his attorney, the service of which is not governed by the other sections of this chapter and which is not otherwise specifically provided for by law, may be given by sending the same by registered mail with proper postage prepaid addressed to the addressee's last known address with request for return receipt, and the production of a returned receipt purporting to be signed by the addressee shall create a disputable presumption that such notice was received by the person to whom the notice was required to be sent.

(b) Electronic service is not authorized for a notice that requires certified or registered mail.