Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail.

Setup

• Install the postfix package and open the firewall for smtp

  $ dnf install -y postfix
  $ firewall-cmd --zone=public --add-service=smtp --permanent
  $ firewall-cmd --reload
  

• Remove sendmail

  $ dnf remove -y sendmail
  

• Set Postfix as the default Mail Transfer Agent

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

Configuration

• Backup

  $ mv /etc/postfix/main.cf /etc/postfix/main.cf.bak
  

• Edit the configuration file

  nano /etc/postfix/main.cf
  
  myhostname = $(hostname -f)
  myorigin = \$myhostname
  inet interfaces = all
  inet protocols = ipv4
  mydestination = \$myhostname, localhost
  mynetworks = 192.168.1.0/24, 127.0.0.0/8 10.0.0.0/24
      
  

• Restart

  $ systemctl enable postfix.service
  $ systemctl start postfix.service
  

Testing

• Install the mailx email client

  $ dnf install -y mailx
  

• Send a test email to your own external email address.
  Update the hostname in the mailx command to match the instance from which you are sending email

  $ hostname=$(hostname -f)
  $ echo "External email" | mailx -r root@$hostname -s "Test email subject" [email protected]
  

• If the email does not appear, you can check the Postfix mail queue

  $ mailq
  $ tail -f /var/log/maillog
  

Using SMTP Relay with sendinblue.com

• Edit main.cf

  $ nano /etc/postfix/main.cf
  
  relayhost = [smtp-relay.sendinblue.com]:587
  
  # outbound relay configurations
  smtp_sasl_auth_enable = yes
  smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
  smtp_sasl_security_options = noanonymous
  smtp_tls_security_level = may
  header_size_limit = 4096000
  
  $ nano /etc/postfix/sasl_passwd
  
  [smtp-relay.sendinblue.com]:587      smtp_username:smtp_password
  
  $ postmap /etc/postfix/sasl_passwd
  $ systemctl restart postfix
  $ chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db