California Code, Probate Code - PROB § 8575

(a) In the event of service by mail, by certificate of the Secretary of State, under official seal, showing the mailing. The certificate shall be filed with the court from which process issued.

(b) In the event of personal service outside this state, by the return of any duly constituted public officer qualified to serve like process, or notice of motion, of and in the jurisdiction where the nonresident personal representative is found, showing the service to have been made. The return shall be attached to the original summons, or notice of motion, and filed with the court from which process issued.