Unless a different time is specified therein or by law, every order made by the public utilities commission shall become effective immediately upon entry thereof upon the journal of the public utilities commission. Every order shall be served by United States mail in the manner prescribed by the commission. No utility or railroad shall be found in violation of any order of the commission until notice of said order has been received by an officer of said utility or railroad, or an agent duly designated by said utility or railroad to accept service of said order.