A deed which purports to convey a greater right or interest in real property than the person making it may lawfully convey shall operate as an alienation of such right or interest in such real property as such person might lawfully convey. The application of the doctrine of estoppel by deed, and the liability of the grantor, his heirs and personal representatives upon the covenants, if any, contained in such conveyance shall be determined according to the rules of law applicable to other deeds.