I just checked the Portal.
https://www.mass.gov/forms/change-of-address-notification-form It says you still need to notify the Police Departments by mail too.
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Change of Address Notification Form
Complete the form below to notify the DCJIS/FRB of an address change for your Massachusetts firearms license.
Pursuant to Massachusetts General Law Chapter 140, sections 129B and 131, a cardholder shall notify the licensing authority that issued such firearms license, the chief of police into whose jurisdiction such card holder moves, and the commissioner of the Department of Criminal Justice Information Services of any change of address within 30 days of its occurrence.
Failure to notify any of these entities shall be cause for revocation or suspension of the license.
In lieu of notifying the FRB/DCJIS via certified mail, you may submit the form below to report your change of address.
All fields must be completed fully and accurately.
Notifications to police departments must still be made in writing via certified mail.
You will not receive a replacement license for this request.