Notwithstanding the preceding sentence, the marital deduction is disallowed under these circumstances only if the other donee, the donor, or the possible appointee, may, by reason of the transfer or retention, possess or enjoy any part of the property after the termination or failure of the interest therein transferred to the donee spouse.
Example. The donor purchased three annuity contracts for the benefit of his wife and himself. The first contract provided for payments to the wife for life, with refund to the donor in case the aggregate payments made to the wife were less than the cost of the contract. The second contract provided for payments to the donor for life, and then to the wife for life if she survived the donor. The third contract provided for payments to the donor and his wife for their joint lives and then to the survivor of them for life. No marital deduction may be taken with respect to the gifts resulting from the purchases of the contracts since, in the case of each contract, the donor may possess or enjoy a part of the property after the termination or failure of the interest transferred to the wife.
Example. The donor, having a power of appointment over certain property, appointed a life estate to his spouse. No marital deduction may be taken with respect to such transfer, since, if the retained power to appoint the remainder interest is exercised, the appointee thereunder may possess or enjoy the property after the termination or failure of the interest taken by the donee spouse.
26 C.F.R. §25.2523(b)-1