Cal. Civil Code § 8118

(a) Proof that notice was given to a person in the manner required by this part shall be made by a proof of notice declaration that states all of the following: (1) The type or description of the notice given. (2) The date, place, and manner of notice, and facts showing that notice was given in the manner required by statute. (3) The name and address of the person to which notice was given, and, if appropriate, the title or capacity in which the person was given notice. (b) If the notice is given by mail, the declaration shall be accompanied by one of the following: (1) Documentation provided by the United States Postal Service showing that payment was made to mail the notice using registered or certified mail, or express mail. (2) Documentation provided by an express service carrier showing that payment was made to send the notice using an overnight delivery service. (3) A return receipt, delivery confirmation, signature confirmation, tracking record, or other proof of delivery or attempted delivery provided by the United States Postal Service, or a photocopy of the record of delivery and receipt maintained by the United States Postal Service, showing the date of delivery and to whom delivered, or in the event of nondelivery, by the returned envelope itself. (4) A tracking record or other documentation provided by an express service carrier showing delivery or attempted delivery of the notice.