Thereupon the court shall fix the time and place for the hearing of such petition and shall direct that notice thereof shall be mailed to each of the known certificate holders, investors and creditors of such insurer affected by such plan and to the trustee or depositary under all mortgage participation trusts created by such insurer and then in existence, together with either a copy of such plan or a summary thereof, which summary shall be either prepared or approved by the commissioner. If the commissioner shall be the proposer of such plan the court shall direct such insurer to deliver to the commissioner a list of the names and addresses of all certificate holders, creditors, investors and other known persons affected by such plan. Said notices shall be mailed, postage prepaid, to the respective addresses as shown on such list, or if no address be there shown, to the last known address.