Section 3C. Service of process under section three A or three B shall be made by leaving a copy of the process with a fee to be determined annually by the commissioner of administration under the provision of section three B of chapter seven in the hands of the registrar, or in his office, and by giving the defendant notice in either the manner provided in paragraph (1) or in that provided in paragraph (2) hereof, and such service shall be sufficient service upon a defendant who has under either of said sections appointed the registrar or his successor his true and lawful attorney therefor.

(1) If the defendant is known by the plaintiff to be the holder of a motor vehicle registration or operator's license issued by another state or country, notice of such service upon the registrar as attorney for the defendant and a copy of the process shall forthwith be sent by registered mail, with return receipt requested, by the plaintiff to the defendant at his address of record in the office from which such registration or license was issued. The plaintiff's affidavit of compliance herewith, and the defendant's return receipt, if received by the plaintiff, shall be filed in the case on or before the return day of the process or within such further time as the court may allow. If the defendant has no motor vehicle registration or license known to the plaintiff, such notice and copy shall be sent in the same manner to the last address of the defendant known to the plaintiff, and affidavit of compliance herewith, and the defendant's return receipt or other proof of actual notice, shall be filed in the case within the time above provided.

(2) Notice of such service upon the registrar and a copy of the process shall be served upon the defendant, if found within the commonwealth, by a sheriff or deputy sheriff of any county of this commonwealth, or, if found without the commonwealth, by any duly constituted public officer qualified to serve like process in the state or jurisdiction where the defendant is found, and the officer's return showing such service to have been made shall be filed in the case on or before the return day of the process or within such further time as the court may allow.

(3) The court in which the action is pending may order such continuances as may be necessary to afford the defendant reasonable opportunity to defend the action.