Mo. Rev. Stat. § 143.831: Notice of director's action.

The director of revenue shall mail notice of his action on the claim for refund within one hundred twenty days of the mailing of such claim. The action denying a claim for refund is final upon the expiration of sixty days from the date when he mails notice of his action to the taxpayer, except only for such amounts as to which the taxpayer has filed a protest with the director of revenue.