From New England First Amendment Center:
Emails dealing with public business sent or received by public officials from their personal email accounts are public records, according to a ruling by the Massachusetts secretary of state.
Frank Bonet, personnel director for Lawrence, asked the city for copies of all emails related to city business that were sent or received by City Councilor Marc Laplante from his personal email account. When the city failed to respond, Bonet filed an appeal with Secretary of State William F. Galvin, who oversees the Massachusetts Public Records Law.