An action of covenant may be maintained on any written conveyance or lease which, under the provisions of section one, article one of this chapter, must be by deed, and which has been executed since the twenty-sixth day of July, nineteen hundred and twenty-one, for the breach of any covenant or warranty or other agreement therein contained, whether such instrument be sealed or unsealed, and every estoppel which would have been created by such writing, if sealed, shall be created by it, though it be unsealed. Such action of covenant may also be maintained upon any contract or agreement for the conveyance of any interest in land, which interest, if conveyed, would be required, by said section one, article one of this chapter, to be conveyed by deed.