Mo. Rev. Stat. § 525.050

Notice of garnishment shall be served on a corporation, in writing, by delivering such notice, or a copy thereof, only to a person designated by the corporation in a registered letter filed with the sheriff or officer for collection in the corporation's county of primary business; provided, if such designated person is not available or if such designation is not filed with the sheriff or officer of collection, then such notice may be served upon the president, secretary, treasurer, cashier or other chief or managing officer of such corporation. Notice of garnishment may be served on railroad corporations by delivering the same, or a copy thereof, to any station or freight agent of such corporation, and on insurance companies not incorporated by or organized under the laws of this state, by delivering the same, or a copy thereof, to the director of the department of commerce and insurance.