Section 11. In addition to and not in limitation of other provision of law, service of process may be made upon the foreign personal representative, guardian or conservator by registered or certified mail, addressed to his last reasonably ascertainable address, requesting a return receipt signed by addressee only. Notice by ordinary first class mail is sufficient if registered or certified mail service to the addressee is unavailable. Service may be made upon a foreign personal representative in the manner in which service could have been made under other laws of the commonwealth on either the foreign personal representative or his decedent immediately prior to death.

If service is made upon a foreign personal representative, guardian or conservator as provided in this section, he shall be allowed at least thirty days within which to appear or respond.