Secure Linux Mail Server

I have a Linux Server with Exim running. I need you to test for vulnerabilities and fix any holes if necessary. I am also receiving NDR's. I need you to evaluate why and stop them at the most logical place. Here is a copy of the ndr: -----Original Message----- From: Mail Delivery System [mailto:] Sent: Sunday, November 04, 2012 6:30 PM To: Subject: Delivery status notification This is an automatically generated Delivery Status Notification. Delivery to the following recipients was aborted after 1 second(s): * [login to view URL] Reporting-MTA: dns; [login to view URL] [[login to view URL]] Received-From-MTA: dns; [login to view URL] [[login to view URL]] Arrival-Date: Sun, 04 Nov 2012 23:29:35 +0000 Final-recipient: rfc822; Action: failed Status: 5.1.1 Diagnostic-Code: smtp; 550 Sender verify failed Last-attempt-Date: Sun, 04 Nov 2012 23:29:36 +0000 [login to view URL] Received: from LENOVO8C85193F ([[login to view URL]]) by [login to view URL] with comcast id KbVH1k00N0JbjDu3UbVHpi; Sun, 04 Nov 2012 23:29:18 +0000 Date: Sun, 4 Nov 2012 18:27:55 -0500 From: "Dennis Rzaca" <> Subject: FW: Rockwall on ebay To: <> Message-id: <04ff01cdbae4$048de3d0$0da9ab70$@net> MIME-version: 1.0 X-Mailer: Microsoft Office Outlook 12.0 Content-type: TEXT/PLAIN Content-language: en-us Content-transfer-encoding: QUOTED-PRINTABLE Thread-index: Ac2632IuI+nlGxQsRWe4IGkK1DCaZwABIdZA X-Authority-Analysis: v=2.1 cv=cchqGRzM c=1 sm=1 tr=0 a=Wsq5XqQU4T7VqR9LJbCV/w==:117 a=Wsq5XqQU4T7VqR9LJbCV/w==:17 a=C_IRinGWAAAA:8 a=rl5eUP2J6s4A:10 a=QWFM8rU1nTkA:10 a=r77TgQKjGQsHNAKrUKIA:9 a=eukT-F3iAAAA:8 a=3SuXiPc-AAAA:8 a=bQEaMyaYAAAA:8 a=c9TJ0esw162PEsUz2CsA:9 a=AOPmnQSjjHqWHHbu:21 a=m88zyXsoTgKBn-eJ:21 a=CjuIK1q_8ugA:10 a=uo4fVnsz2jAA:10 a=h9FQ92UpsxwA:10 a=zngGcj2eKycA:10 a=vJKAHVnifBAA:10 a=si9q_4b84H0A:10 a=r5sAVyOHGskA:10 a=yMhMjlubAAAA:8 a=SSmOFEACAAAA:8 a=EKubPk50ZT8oioXCwpIA:9 a=AVKMXY_jzXeuJxUu:21 a=uFE6fm01H7wPOmei:21 a=ydFImBEFDtVcYJTo:21 a=gKO2Hq4RSVkA:10 a=UiCQ7L4-1S4A:10 a=hTZeC7Yk6K0A:10 a=frz4AuCg-hUA:10 a=YWwL-17czsxpwUa8rlMA:9 a=bTx1VQQ7nYRB8fjt:21 a=B2IU8pO732cxsa7x:21 a=KIncT2mZeoqYwPAT:18 a=HXjIzolwW10A:10 Attached Message Part