POSTFIX Postfix is a free open source mail transfer agent (MTA), a computer program for the routing and delivery of email. It is intended as a fast, easy-to-administer, and secure alternative to the widely-used Sendmail MTA which is installed by default with CentOS. First we need to remove the Sendmail MTA yum remove sendmail Install Postfix yum install postfix Installation Of Required Packages for SMTP AUTH yum install cyrus-sasl cyrus-sasl-devel cyrus-sasl-gssapi cyrus-sasl-md5 cyrus-sasl-plain Postfix configuration files are stored in /etc/postfix. The two main postfix configuration files are master.cf and main.cf. First we are going to make some additions or changes to the main.cf configuration file as below #NOTE: Make sure you uncomment inet_interfaces = localhost home_mailbox = Maildir/ mailbox_command = mynetworks = 127.0.0.0/8,221.132.35.94 inet_interfaces = all mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain relay_domains = l