Dovecot on RHEL/CentOS based distributions

If you have installed the Postfix mail server to
operate as the Simple Mail Transfer Protocol (SMTP) service on an
email server, you might still need a way to retrieve the incoming mail
from the server.

This article shows you how to install and configure Dovecot, an
open-source Internet Message Access Protocol (IMAP) and Post Office Protocol
version 3 (POP3) server application designed specifically for Linux® and
UNIX® operating systems. Dovecot retrieves emails from Postfix and
delivers them to the relevant mailbox on the server.

You can get your mail through Dovecot by using either the POP3 or the IMAP
protocol.

Prerequisites

You need the following operating system and software to use Dovecot:

• A CentOS® 7.0 or later Linux distribution
• Postfix

Install Dovecot

Download and install the Dovecot package by running the following command:

$ sudo yum install dovecot -y

NOTE: For CentOS 8 The only difference is that 8 versions (RHEL 8 / Alma Linux 8 / Rocky Linux 8) is that this versions uses dnf instead of yum.

For instalation process, use the following command:

$ sudo dnf -y install dovecot

It is the only difference, the exact same process it's necesarry after execute this command

Configure Dovecot

Once the installation finished, you need to configure the services in the
configuration file at /etc/dovecot/dovecot.conf. This example uses
the vi text editor, but you can use any text editor that you want.

1- Use the following command to open the file in vi:

$ sudo vi /etc/dovecot/dovecot.conf

2- Uncomment the following lines in the file and, if necessary, change them to
reflect your plans for the environment:

protocols = imap pop3
listen = *, ::

Configure the location of the Mailbox

Next you need to configure the location of the Mailbox file,

1- Use the following command to open the file in vi:

$ sudo vi /etc/dovecot/conf.d/10-mail.conf

2- Uncomment the following line in the file and, if necessary, change them to
reflect your plans for your environment:

mail_location = maildir:~/Maildir

Configure Postfix SMTP authentication

You can set the location for your mail by editing the configuration file at
/etc/dovecot/conf.d/10-master.conf.

1- Use the following command to open the file in vi:

sudo vi /etc/dovecot/conf.d/10-master.conf

2- Either add or uncomment the following line in the configuration file:

m unix_listener /var/spool/postfix/private/auth{
       mode = 0666
       user = postfix
       group = postfix
       }

Configure POP3

Finally, configure the /etc/dovecot/conf.d/20-pop3.conf file, which enables
older and less popular email clients to connect and transmit messages
correctly.

1- Use the following command to open this file in nano:

sudo nano /etc/dovecot/conf.d/20-pop3.conf

2- Uncomment or add the following lines:

pop3_uidl_format = %08Xu%08Xv
pop3_client_workarounds = outlook-no-nuls oe-ns-eoh

Create a mailbox

The example in this section adds a mailbox that a hypothetical user named Joe
Bloggs (joe.bloggs) can use to send and receive emails.

You can create a user for this example, or you can use an existing user.

1- If necessary, use the following command to make a new user:

sudo useradd joe.bloggs

2- Use the following command to create the mail directory for your user:

sudo mkdir /home/joe.bloggs/Maildir

3- Give ownership of the mailbox that you just created to joe.bloggs by
changing its permissions:

sudo chown joe.bloggs:joe.bloggs /home/joe.bloggs/Maildir
sudo chmod -R 700 /home/joe.bloggs/Maildir

Start Dovecot

Use the following steps to start the Dovecot service:

1- Use the following chkconfig command to verify that the Dovecot
application will run when the server is restarted:

sudo chkconfig --level 345 dovecot on

2- Use the following command to start the Dovecot service:

sudo service dovecot start

Configure Postfix

Next, you need to configure Postfix to enable your email client to connect to
your new SMTP server.

1- Use the following command to open the file at /etc/postfix/main.cf in
vi:

sudo vi /etc/postfix/main.cf

2- Add the following lines to the file:

smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_local_domain = $myhostname
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks, reject_unauth_destination
broken_sasl_auth_clients = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth

3- After you have added the preceding lines, exit the main.cf file and
restart the Postfix service by using the following command:

sudo service postfix restart

Add ports to iptables

Now that you have enabled secure SMTP Secure Sockets Layer (SSL), you should
allow connections to port 587 by opening the port for your server in iptables.

1- Add the rule for this port by entering the following command:

sudo iptables -I INPUT 2 -p tcp --dport 587 -j ACCEPT

2- Add the POP and IMAP ports, as well as their secure counterparts:

sudo iptables -I INPUT 3 -p tcp --dport 110 -j ACCEPT
sudo iptables -I INPUT 4 -p tcp --dport 143 -j ACCEPT
sudo iptables -I INPUT 5 -p tcp --dport 993 -j ACCEPT
sudo iptables -I INPUT 6 -p tcp --dport 995 -j ACCEPT

3- Use the following commands to save the iptables rules and restart iptables:

sudo /etc/init.d/iptables save
sudo /etc/init.d/iptables restart

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