Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 159, § 5

Every association of persons who are not inhabitants of this commonwealth which does an express business therein shall in writing appoint a person, who is a citizen and a resident thereof, to be a general agent, upon whom all lawful processes against such persons may be served with like effect as if served on said persons; and said writing or power of attorney shall contain an agreement on the part of the persons making it that the service of any lawful process against it or them on said general agent shall be of the same legal force and validity as such service on said persons or any of them. The power of attorney shall be filed in the office of the state secretary, and copies certified by him shall be taken as sufficient evidence and proof thereof. Such agency shall be continued so long as such express business is done in this commonwealth, and the power of attorney shall not be revoked until a similar power is given to another person and filed as aforesaid.