In MA, does filing a responsive pleading in a case submit to jurisdiction/service?

You seek legal advice on an issue where the answer can turn on slight variance in the facts. Hire an attorney to review all of the facts so as to properly opine on what you perceive to be the issue (and any others that may be present).

I agree with the other lawyer that this is a fact-specific question. But in general, to point you in the right direction: 1. Under Mass. R. Civ. P. 12(b)(5), insufficient service of process is an affirmative defense that the defendant must plead in response to the complaint. 2. It sounds like your case may involve a corporate defendant that is not represented by a lawyer. Under Varney Enterprises, Inc. v. WMF, Inc., 402 Mass. 79 (1988): "except for small claim matters, a corporation may not be represented in judicial proceedings by a corporate officer who is not an attorney licensed to practice law in the Commonwealth." 3. You may want to confirm whether service was made on the registered agent, as shown on the Secretary of State's website. Good luck, and if this case is important to you, review it with a lawyer.