Mass. Gen. Laws ch. 204 § 30
If a power of appointment releasable according to section twenty-seven, or under common law, is or may be exercisable by two or more persons in conjunction with one another or successively, a release of the power, in whole or in part, executed, and delivered or filed, in accordance with the first sentence of section twenty-eight, by any one of the donees of the power, shall, subject to the second sentence of section twenty-eight, be effective to release, to the extent therein provided, all right of such person to exercise or to participate in the exercise of the power, but, unless the instrument creating the power otherwise provides, shall not prevent or limit the exercise or participation in the exercise thereof by the other donee or donees thereof.
Mass. Gen. Laws ch. 204, § 30