Mass. Gen. Laws ch. 244, § 18: Persons authorized to redeem

Section 18. The mortgagor or person claiming or holding under him may, after breach of condition, redeem the land mortgaged, unless the mortgagee, or person claiming or holding under him, has obtained possession of the land for breach of condition and has continued that possession for three years, or unless the land has been sold pursuant to a power of sale contained in the mortgage deed.