Sendmail is currently sending out notifications from prdapp01 and prdapp02. The current headers from prdapp01 as follows - Return-Path: Received: from 10-166-152-11.cloud.opsource.net ([207.20.54.3]) by mx.google.com with ESMTPS id o17si732085vct.60.2015.01.15.21.47.39 for (version=TLSv1 cipher=RC4-SHA bits=128/128); The current headers from prdapp02 as follows - Return-Path: Received: from 10-166-152-19.cloud.opsource.net ([207.20.45.152]) by mx.google.com with ESMTPS id f13si4781217qaa.86.2015.01.15.21.49.30 for (version=TLSv1 cipher=RC4-SHA bits=128/128); The proposed changes are to do the following - **DNS changes**\\ Add the DNS entry for A host as mail01.learnexa.com - 207.20.45.3\\ Add the DNS entry for A host as mail02.learnexa.com - 207.20.45.152\\ **Verify Ports and their impact**\\ verify nmap -v 207.20.45.3 to see the ports which are open in prdapp01 and verify the impact.\\ verify nmap -v 207.20.45.152 to see the ports which are open in prdapp02 and verify the impact.\\ **on prdapp01**\\ yum install sendmail-cf\\ change the sendmail configuration as follows - backup sendmail.cf\\ go to sendmail.mc\\ add the line below\\ define(`confDOMAIN_NAME', `mail01.learnexa.com')dnl\\ (this is not explicitly defined at this time and therefore the system name is being used by default)\\ m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf\\ /etc/init.d/sendmail restart\\ Test by sending an email using mutt and verify that the headers are reflecting the new change.\\ **on prdapp02**\\ yum install sendmail-cf\\ change the sendmail configuration as follows - go to sendmail.mc\\ add the line below\\ define(`confDOMAIN_NAME', `mail02.learnexa.com')dnl\\ (this is not explicitly defined at this time and therefore the system name is being used by default)\\ m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf\\ /etc/init.d/sendmail restart\\ Test by sending an email using mutt and verify that the headers are reflecting the new change.