Mo. Rev. Stat. § 472.110
Proof of service in all cases requiring notice whether by publication, mailing or otherwise, shall be filed before the hearing. Service made by a private person shall be proved by the affidavit of the person or by acknowledgment of service; service made by the clerk, sheriff or other official shall be proved by certificate or return of service. Proof of service by publication shall be made in the form of the affidavit prescribed by section 493.060. In the case of service by registered or certified mail, where the court requires a return receipt, the return receipt shall be attached to the proof of service if a receipt has been received; if no receipt has been received, or in case a notice served by ordinary mail is returned to the sender, the court may, in its discretion, order further service on the party.
§ 472.110, RSMo
Effective 1/1/1981