Section 6A. Every application under sections three to five, inclusive, for a transient vendor’s license shall contain an irrevocable power of attorney, in such form as the deputy director may prescribe, constituting and appointing, in case the license applied for is issued, the deputy director, or his successors in office, the true and lawful attorney of the applicant upon whom may be served all lawful process in any action or proceeding against him growing out of the transaction of business by him within this commonwealth under the license, and containing an agreement that any process against him which is so served shall, if he is notified of such service as hereinafter provided, be of the same legal force and validity as if served on him personally and that the mailing by the deputy director of a copy of such process to him at his last address as appearing on the deputy director’s records shall be sufficient notice to him of such service. Service of such process shall be made by leaving duplicate copies thereof with a fee, as determined annually by the commissioner of administration under the provision of section three B of chapter seven, in the hands of the deputy director, or in his office, and the deputy director shall forthwith send one of said copies by mail, postage prepaid; addressed to the defendant at his last address as appearing on the deputy director’s records; and an affidavit of the deputy director, or of any person authorized by him to send such copy, that such copy has been so mailed shall be prima facie evidence thereof. One of the duplicates of such process, certified by the deputy director as having been served upon him, shall be sufficient evidence of service upon him under said power of attorney. 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.