Missouri Revised Statutes Title IX. Suffrage and Elections § 115.652. Mail-in voting may be conducted, when

(1) The officer or agency calling the election submits a written request that the election be conducted by mail. Such request shall be submitted not later than the date specified in section 115.125 for submission of the notice of election and sample ballot;

(2) The election authority responsible for conducting the election authorizes the use of mailed ballots for the election;

(3) The election is nonpartisan;

(4) The election is not one at which any candidate is elected, retained or recalled; and

(5) The election is an issue election at which all of the qualified voters of any one political subdivision are the only voters eligible to vote.