Mo. Rev. Stat. § 351.376: Resignation of agent.

Any registered agent of a corporation may resign as such agent upon filing a written notice thereof, executed in duplicate, with the secretary of state, who shall forthwith mail the copy thereof to any officer of the corporation at his address as last known to the secretary of state, other than such registered office. Such resignation shall become effective upon the expiration of thirty days after receipt of such notice by the secretary of state.