California Code, Elections Code - ELEC § 16442

After the affidavit is filed with the clerk of the superior court, a copy of the affidavit shall be personally served upon the defendant or sent to him or her by registered mail in a sealed envelope with postage prepaid, addressed to the defendant at the place of residence named in his or her affidavit of registration. The contestant shall make an affidavit of mailing if he or she serves the affidavit by mail, and file it on the same day with the county elections official.