This tutorial will help you to setup DomainKeys and postfix configuration on Centos server. Install EPEL repository: 64 bit: # rpm -Uvh http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-7.noarch.rpm 32 bit: # rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-7.noarch.rpm Install DKIM: # yum install opendkim # mkdir /etc/opendkim/keys/linuxpcfix.com # export domain=linuxpcfix.com # cd /etc/opendkim/keys/linuxpcfix.com Generate Private keys as...