Mo. Rev. Stat. § 138.433
Current with changes from the 2023 Legislative Session
In determining whether pleadings are filed within the time allowed by law, such pleadings may be transmitted to the state tax commission by registered mail. Pleadings so filed shall be deemed filed with the commission as of the date deposited with the United States Postal Service as shown by the record of such mailing.
§ 138.433, RSMo