California Code, Government Code - GOV § 11440.20

(a) The writing, electronic document, or notice shall be delivered personally or sent by mail, electronic, or other means to the person at the person's last known address or, if the person is a party with an attorney or other authorized representative of record in the proceeding, to the party's attorney or other authorized representative.  If a party is required by statute or regulation to maintain an address with an agency, the party's last known address is the address maintained with the agency.

(b) Unless a provision specifies the form of mail, service or notice by mail may be by first-class mail, registered mail, or certified mail, by mail delivery service, by facsimile transmission if complete and without error, or by other electronic means as provided by regulation, in the discretion of the sender.