Postfix : installation and configuration

Postfix is an open source mail server, also known as a Mail Transfer Agent (MTA), which relays mail locally or to a destination server outside the network.

In this post guide, we will cover how to install Postfix on RHEL 8 / CentOS 8.

Step 1: Uninstalling Sendmail

First you need to check whether sendmail is already installed :

[root@mail ~]# rpm -qa | grep sendmail

If it is installed, you will get an output similar to that shown below :

[root@mail ~]# rpm -qa | grep sendmail
sendmail-8.14.7-6.el7.x86_64

If nothing is displayed, that’s mean sendmail is not installed.

To uninstall sendmail use the dnf command bellow :

[root@mail ~]# dnf remove sendmail
Loaded plugins: fastestmirror
Resolving Dependencies
--> Running transaction check
---> Package sendmail.x86_64 0:8.14.7-6.el7 will be erased
--> Finished Dependency Resolution
Dependencies Resolved
========================================================================================================================================================================
Package Arch Version Repository Size
Removing:
sendmail x86_64 8.14.7-6.el7 @base 1.7 M
Transaction Summary
Remove 1 Package
Installed size: 1.7 M
Is this ok [y/N]:

Installing Postfix

The Postfix configuration file is /etc/postfix/main.cf , we need to edit this file to make the configuration :

[root@mail ~]# vim /etc/postfix/main.cf

Uncomment the lines below and change the values to match your environment :

myhostname = smtp.mondomain.lan
mydomain = mondomain.local
myorigin = $mydomain
inet_interfaces = all
inet_protocols = all
mydestination = $myhostname, localhost.$mydomain, localhost,
mynetworks = 192.168.2.0/24, 127.0.0.0/8
home_mailbox = Maildir/

Then restart the service :

[root@mail ~]# systemctl restart postfix.service
[root@mail ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: active (running) since Sat 2021-07-17 13:11:38 EDT; 7s ago
Process: 10150 ExecStop=/usr/sbin/postfix stop (code=exited, status=0/SUCCESS)
Process: 10165 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS)
Process: 10163 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
Process: 10159 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS)
Main PID: 10237 (master)
CGroup: /system.slice/postfix.service
├─10237 /usr/libexec/postfix/master -w
├─10238 pickup -l -t unix -u
└─10239 qmgr -l -t unix -u
Jul 17 13:11:38 mail systemd[1]: Stopped Postfix Mail Transport Agent.
Jul 17 13:11:38 mail systemd[1]: Starting Postfix Mail Transport Agent…
Jul 17 13:11:38 mail postfix/master[10237]: daemon started -- version 2.10.1, configuration /etc/postfix
Jul 17 13:11:38 mail systemd[1]: Started Postfix Mail Transport Agent.

Testing the server

Create a test user ( testuser in my case ) :

[root@mail ~]# useradd testuser

[root@mail ~]# cat /etc/passwd |grep testuser
testuserx:x:1000:1000::/home/testuser:/bin/bash

Check server access via telnet :

[root@mail ~]# telnet localhost smtp
Trying ::1…
Connected to localhost.
Escape character is '^]'.
220 mail.localdomain ESMTP Postfix

Then send a test e-mail to an e-mail address with the command mail :

[root@mail ~]# echo "Contenu de mon mail" | mail -s "Sujet" adresse@courriel.fr

If your recipient has received the message, your postfix server is up and running.