Miss. Code § 27-9-49
If, upon examination of any return made under this chapter, it appears that an amount of estate tax, interest or penalties has been paid in excess of that properly due, then the amount in excess shall be immediately refunded to the executor at such time as the commissioner has completed his investigation and has determined the correct estate tax liability of the estate.
If the liability of an estate for estate taxes is contested with the federal government and, as a result of that contest, the commissioner determines that the Mississippi estate tax, interest or penalties have been overpaid, then the overpayment shall be promptly refunded to the executor upon receipt of the federal closing letter or the decision of the tax court in lieu of the federal closing letter.
A refund of estate tax, interest or penalties made pursuant to this chapter shall bear interest at the rate of one-half of one percent (1/2 of 1%) per month, or major fraction thereof, for the period which is the later of the due date of the estate tax return inclusive of all approved extensions, or the final payment of the estate tax, interest or penalty and continuing until the date the commission has completed its investigation and has determined that a refund is due.
If any claim for overpayment of estate tax, interest or penalty is denied, the executor may appeal such decision to the board of review as provided by law.
Miss. Code § 27-9-49