Mo. Rev. Stat. § 92.765
Affidavits of publication of notice of foreclosure, and of posting, mailing, or other acts required by the provisions of sections 92.700 to 92.920 shall be filed in the office of the circuit clerk prior to the trial, and when so filed shall constitute part of the evidentiary documents in the foreclosure suit. Such affidavits shall be prima facie evidence of the performance of acts therein described, and may be so used in the trial of the suit, unless challenged by verified answer duly filed in the suit. The collector shall file with the court an affidavit of compliance with notice requirements of sections 92.700 to 92.920 prior to any sheriff's sale. The affidavit shall include the identities of all parties to whom notice was attempted and by what means. In the case of mailed notice returned undeliverable, the collector's affidavit shall certify that additional notice was attempted and by what means. The expense of complying with this section shall be taxed and collected as other costs in the suit.
§ 92.765, RSMo