Mo. Rev. Stat. § 139.060
It shall be the duty of the collector to furnish to all nonresident taxpayers a statement of the amount of taxes assessed against any tract of land or town lot in his county for any year or years during which he is collector, and send the same by mail to the address of any person applying to him by letter for the same; and if no taxes are due on any such tracts or lots, he shall answer such letters of inquiry, stating the fact; and whenever any funds are remitted by mail or otherwise to any collector for the payment of any taxes appearing to be due on his tax book, it shall be his duty to receive the same and send a receipt therefor by mail to the person remitting the same; provided, that he may charge all sums which he may have to pay for postage as costs against the person applying or remitting to him, but no other costs.
§ 139.060, RSMo