(a) All final decisions and orders of the agency shall be in writing and shall be signed by the president or other presiding member and secretary of the board.(b) All parties shall be notified either personally or by first class mail of any decision or order.(c) On issuance of a decision or order or an order ruling on a motion for rehearing, the agency shall send a copy of the decision or order by first class mail to the attorneys of record or, if a party is not represented by an attorney, to the party, and shall keep an appropriate record of the mailing. A party or attorney of record notified by mail is presumed to have been notified on the third day after the date on which the notice is mailed.