Mississippi Code Title 11. Civil Practice and Procedure § 11-9-125

The defendant in any action shall, on or before the return day of the summons, and before the trial of the case, file with the justice court judge to whom the case is assigned the evidence of debt, statement of account, or other written statement of the claim, if any, which he may desire to and which lawfully may be set off against the demand of the plaintiff, and, in default thereof, he shall not be permitted to use it on the trial.