Section 60B. If any person fails to comply with the requirements of section sixty A he shall be deemed to have appointed said city or town clerk as his agent as above, and service upon any such clerk shall have the same force and effect as service upon such person's duly constituted appointee.
When legal process against any such person is served upon such clerk, a copy of said process shall also forthwith be sent by the plaintiff or his attorney to the defendant at his last known address or to the address last listed for the owner of said premises on the assessors list in said city or town.
Such copy shall be sent by registered mail with return receipt requested. The plaintiff's affidavit of compliance herewith, and the defendant's return receipt, if received by the plaintiff, shall be filed in the court where the case is pending or where the service was issued on or before the return day of the process or within such further time as the court may allow.