Legal Question in Real Estate Law in Massachusetts

Assuming you provided the landlord with your new address in writing, all you have to do is file a complaint for the security deposit and ask the court for treble damages,

If you have not provided the landlord with your new address in writing, then send him a certified letter and a regular letter informing him of your address and demand that he send you your entire security deposit back. A landlord has 30 days from the date you vacate the premises to return your security deposit less any claims for damages. If you do not agree to the claims, the landlord must sue you to keep the security deposit. You should object to any unreasonable charges in writing.

I'd also add that attorneys fees are mandatory where a Security Deposit Violation is found, so you have nothing to lose by hiring an attorney to help you with this. We would take a good security deposit case for no up-front fee.