The term “executor” wherever it is used in this title in connection with the estate tax imposed by this chapter means the executor or administrator of the decedent, or, if there is no executor or administrator appointed, qualified, and acting within the United States, then any person in actual or constructive possession of any property of the decedent.

If the tax or any part thereof is paid by, or collected out of, that part of the estate passing to or in the possession of any person other than the executor in his capacity as such, such person shall be entitled to reimbursement out of any part of the estate still undistributed or by a just and equitable contribution by the persons whose interest in the estate of the decedent would have been reduced if the tax had been paid before the distribution of the estate or whose interest is subject to equal or prior liability for the payment of taxes, debts, or other charges against the estate, it being the purpose and intent of this chapter that so far as is practicable and unless otherwise directed by the will of the decedent the tax shall be paid out of the estate before its distribution.

Unless the decedent directs otherwise in his will, if any part of the gross estate on which tax has been paid consists of proceeds of policies of insurance on the life of the decedent receivable by a beneficiary other than the executor, the executor shall be entitled to recover from such beneficiary such portion of the total tax paid as the proceeds of such policies bear to the taxable estate. If there is more than one such beneficiary, the executor shall be entitled to recover from such beneficiaries in the same ratio. In the case of such proceeds receivable by the surviving spouse of the decedent for which a deduction is allowed under section 2056 (relating to marital deduction), this section shall not apply to such proceeds except as to the amount thereof in excess of the aggregate amount of the marital deductions allowed under such section.

Unless the decedent directs otherwise in his will, if any part of the gross estate on which the tax has been paid consists of the value of property included in the gross estate under section 2041, the executor shall be entitled to recover from the person receiving such property by reason of the exercise, nonexercise, or release of a power of appointment such portion of the total tax paid as the value of such property bears to the taxable estate. If there is more than one such person, the executor shall be entitled to recover from such persons in the same ratio. In the case of such property received by the surviving spouse of the decedent for which a deduction is allowed under section 2056 (relating to marital deduction), this section shall not apply to such property except as to the value thereof reduced by an amount equal to the excess of the aggregate amount of the marital deductions allowed under section 2056 over the amount of proceeds of insurance upon the life of the decedent receivable by the surviving spouse for which proceeds a marital deduction is allowed under such section.

A decedent who was a citizen of the United States and a resident of a possession thereof at the time of his death shall, for purposes of the tax imposed by this chapter, be considered a “citizen” of the United States within the meaning of that term wherever used in this title unless he acquired his United States citizenship solely by reason of (1) his being a citizen of such possession of the United States, or (2) his birth or residence within such possession of the United States.

A decedent who was a citizen of the United States and a resident of a possession thereof at the time of his death shall, for purposes of the tax imposed by this chapter, be considered a “nonresident not a citizen of the United States” within the meaning of that term wherever used in this title, but only if such person acquired his United States citizenship solely by reason of (1) his being a citizen of such possession of the United States, or (2) his birth or residence within such possession of the United States.