WAC 388-107-1570
WAC 388-107-1570. Notice — Proof of service
The department may establish proof of service by any of the following:
(1) A declaration of personal service;
(2) An affidavit or certificate of mailing to the enhanced services facility or to the individual to whom notice is directed;
(3) A signed receipt from the person who accepted the certified mail, the commercial delivery service, or the legal messenger service package; or
(4) Proof of fax transmission.