The law in plain English
Return deadline
Under Mass. Gen. Laws ch. 186, Section 15B, the deposit response usually has to be sent within 30 days of the move-out timeline described by the state rule.
Required notice
Massachusetts generally gives the landlord 30 days to return the deposit or send a compliant itemized statement, and statutory violations can trigger mandatory treble damages.
This dispute type
Once the Massachusetts deadline passes, the dispute stops being only about the deductions and becomes a deadline-compliance problem too. A landlord may still argue damage existed, but Mass. Gen. Laws ch. 186, § 15B sets the clock for returning the balance and explaining any amount withheld.
Penalty leverage
If the withholding was wrongful or in bad faith, the exposure allowed under the statute is: 3x the deposit, plus interest, court costs, and reasonable attorney's fees