Cal. Civ. Proc. Code § 706.080

Service of a withholding order for taxes or of any other notice or document required under this chapter in connection with a withholding order for taxes may be made by the state by first-class mail, postage prepaid, or by any authorized state employee. Service of a withholding order for taxes is complete when it is received by the employer or a person described in paragraph (1) or (2) of subdivision (a) of Section 706.101. Service of, or the providing of, any other notice or document required to be served or provided under this chapter in connection with a withholding order for taxes is complete when the notice or document is deposited in the mail addressed to the last known address of the person on whom it is served or to whom it is to be provided.