How to Install Postfix on CentOS/RHEL 7/6/5

Postfix is fast and popular SMTP server widely used. The main job of postfix is to relay mail locally or to the intended destination outside the network. Some of the most popular SMTP servers are Sendmail, Postfix, and Qmail. By default, Sendmail comes pre-installed with CentOS/RHEL 5. We will need to remove it and install Postfix.

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Step 1 – Install Postfix

If Postfix not already installed on your machine, Install it using the following command. Also, remove sendmail if already installed.

yum remove sendmail
yum install postfix

Make postfix as default MTA for your system using the following command

alternatives --set mta /usr/sbin/postfix

If above command not work and you get the output as “/usr/sbin/postfix has not been configured as an alternative for mta“. Use below command to do the same else skip it

alternatives --set mta /usr/sbin/sendmail.postfix

Step 2 – Configure Postfix

Let’s start postfix configuration. Edit Postfix configuration file /etc/postfix/main.cf in your favorite editor and make following changes.

  myhostname = mail.tecadmin.net
  mydomain = tecadmin.net
  myorigin = $mydomain
  inet_interfaces = all
  mydestination = $myhostname, localhost, $mydomain
  mynetworks = 127.0.0.0/8, /32
  relay_domains = $mydestination
  home_mailbox = Maildir/

After executing above command edit the postfix configuration file and make sure all changes are done properly.

Step 3 – Restart Postfix Service

As we have done basic Postfix configuration, So restart Postfix service to read changes of configuration. Also, configure to autostart on system boot.

service postfix restart
chkconfig postfix on

Step 4 – Open Firewall Port

Now if your system is configured to use iptables firewall, So add firewall rules to make postfix accessible from outside, using following commands.

iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 25 -j ACCEPT
iptables -A INPUT -m state --state NEW -m udp -p udp --dport 25 -j ACCEPT

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