Whenever in this chapter written notification is prescribed, which shall include the filing of a petition for reconsideration, the notification shall be made by depositing the papers in the post office, properly addressed, with postage prepaid. Whenever in this chapter written notification is required to be given by the department, such notification shall be by certified mail. Any written notice shall be deemed received upon the third day following the day upon which the notice is placed in the mail, unless the third day falls on a Saturday, Sunday or legal holiday, in which event the notice shall be deemed received on the first day other than a Saturday, Sunday or legal holiday, following the third day. Legal holidays are prescribed in RCW 1.16.050.