Missouri Revised Statutes Title XVIII. Labor and Industrial Relations § 288.240. Papers, deemed filed, when

Any notice of appeal, application or other paper required under this law to be filed with the division or the commission shall, when mailed to and received by the division or the commission, be deemed to be filed as of the date endorsed by the United States post office on the envelope or container in which such paper is received. In instances where the last day for the filing of any such paper falls on a Saturday, Sunday, or legal holiday, the filing shall be deemed timely if accomplished on the next day which is neither a Saturday, Sunday, nor a legal holiday.