Cal. Code of Civil Procedure § 415.30

(a) A summons may be served by mail as provided in this section. A copy of the summons and of the complaint shall be mailed (by first-class mail or airmail, postage prepaid) to the person to be served, together with two copies of the notice and acknowledgment provided for in subdivision (b) and a return envelope, postage prepaid, addressed to the sender. (b) The notice specified in subdivision (a) shall be in substantially the following form: (Title of court and cause, with action number, to be inserted by the sender prior to mailing)NOTICE To: (Here state the name of the person to be served.) This summons is served pursuant to Section 415.30 of the California Code of Civil Procedure. Failure to complete this form and return it to the sender within 20 days may subject you (or the party on whose behalf you are being served) to liability for the payment of any expenses incurred in serving a summons upon you in any other manner permitted by law. If you are served on behalf of a corporation, unincorporated association (including a partnership), or other entity, this form must be signed in the name of such entity by you or by a person authorized to receive service of process on behalf of such entity. In all other cases, this form must be signed by you personally or by a person authorized by you to acknowledge receipt of summons. Section 415.30 provides that this summons is deemed served on the date of execution of an acknowledgment of receipt of summons. Signature of sender ACKNOWLEDGMENT OF RECEIPT OF SUMMONS This acknowledges receipt on (insert date) of a copy of the summons and of the complaint at (insert address). Date: (Date this acknowledgement is executed) Signature of person acknowledging receipt, with title ifacknowledgment is made on behalf of another person (c) Service of a summons pursuant to this section is deemed complete on the date a written acknowledgement of receipt of summons is executed, if such acknowledgement thereafter is returned to the sender. (d) If the person to whom a copy of the summons and of the complaint are mailed pursuant to this section fails to complete and return the acknowledgement form set forth in subdivision (b) within 20 days from the date of such mailing, the party to whom the summons was mailed shall be liable for reasonable expenses thereafter incurred in serving or attempting to serve the party by another method permitted by this chapter, and, except for good cause shown, the court in which the action is pending, upon motion, with or without notice, shall award the party such expenses whether or not he is otherwise entitled to recover his costs in the action. (e) A notice or acknowledgment of receipt in form approved by the Judicial Council is deemed to comply with this section.