Complaints, decisions and orders and other processes and papers of the board and agent may be served personally, by registered or certified mail or by leaving a copy thereof in the principal office or place of business of persons to be served. The verified return by the individual so serving the same, setting forth the manner of such service, shall be proof of the same and the return post office receipt, when registered or certified and mailed as aforesaid, shall be proof of service of the same.
Conn. Agencies Regs. § 31-101-74