Metropolitan Credit Union v. Matthes, 46 Mass. App. Ct. 326 (1999) ruled that an oral agreement to give a partial release was unenforceable, because it would be "a contract for the sale of lands, tenements or hereditaments" or of some "interest in or concerning them," and would have to be in writing under the Statute of Frauds.
Sometimes a mortgagor will be able to negotiate at the time the mortgage is given and have included in the terms of the mortgage a provision that the mortgagee will give partial releases as, when and if parcels are sold, upon the payment of a designated sum. But in Eno & Hovey, Real Estate Law with Forms (Fourth Edition, 2004), §9.54 (footnote 1) the authors pose the question: A Since a mortgage ordinarily is signed only by a mortgagor, is a mortgagee held to a promise not signed by the mortgagee? In any event, whether such a provision is enforceable notwithstanding the lack of the mortgagee's signature, it is not enforceable while the mortgage is in default. Rhode Island Hosp. Trust Natl. Bank v. Post, 27 Mass. App. Ct. 1207 (1989).