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Dovecot installation and configuration on CentOS


Introduction

If you've installed postfix to operate as the SMTP service on a would-be email server you might still need a way to retrieve the incoming mail from your server.

To that end, in this article we'll talk about installing and configuring Dovecot.

Dovecot is an open-source IMAP and POP3 server application which was designed specifically for Linux/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 using either of the POP3 or IMAP protocols.

Prerequisites

  • Operating System and version: Linux - CentOS 6.0 and above.
  • Postfix installed.
  • Intended purpose for document: Basic installation and configuration of Dovecot.
  • Target Audience: System Administrators, Mail Administrators, Postmasters.

Installation

The first thing we will need is to download the Dovecot package. This command will install it:

sudo yum install dovecot

Configuring Dovecot

The next step is to configure the Dovecot services in the config file at /etc/dovecot/dovecot.conf - use whatever editor you like for the task.

sudo nano /etc/dovecot/dovecot.conf

The following lines will need to be uncommented and if necessary changed to reflect your plans for the environment:

protocols = imap pop3
mail_location =  maildir:~/Maildir
  • protocols - This specifies the protocols that are available for users to access their email.
  • mail_location - This specifies the format and the location of each user's mailbox.

Authentication process file

Next we will configure the authentication process file. This config file can be located at /etc/dovecot/conf.d/10-auth.conf - use the text editor of your choice for this task.

sudo nano /etc/dovecot/conf.d/10-auth.conf

The following line will need to be uncommented and if necessary changed to reflect your plans for your environment:

auth_mechanisms = plain login
  • auth_mechanisms - This specifies the way in which the email client authenticates with Dovecot.

Mail location

To set the location for your mail use the configuration file at /etc/dovecot/conf.d/10-mail.conf.

sudo nano /etc/dovecot/conf.d/10-mail.conf

Either add or uncomment the line below in the configuration file.

mail_location = maildir:~/Maildir

Postfix smtp-auth

Next change the configuration file to configure the unix socket for postfix smtp-auth.  This can be found at /etc/dovecot/conf.d/10-master.conf

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

Comment out the below lines first.

#unix_listener auth-userdb {
    #mode = 0600
    #user =
    #group =
  #}

Now edit these lines in the same file.

# Postfix smtp-auth
  unix_listener /var/spool/postfix/private/auth {
    mode = 0666
    user = postfix
    group = postfix
  }

POP3 configuration

Finally we need to configure the pop3.conf file.  This will allow some older or lesser-used email clients to connect and transmit correctly.  This file can be found at /etc/dovecot/conf.d/20-pop3.conf.

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

We will now need to uncomment or add the following lines.

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

Creating a Mailbox

Now we'll add an example mailbox for a user Joe Bloggs (joe.bloggs) to send and receive emails.

You may need to create a user for this example, or you can use an existing user. To make a new one:

sudo useradd joe.bloggs

You'll need to create the mail directory for your user.

sudo mkdir /home/joe.bloggs/Maildir

Next we need to give joe.bloggs ownership of the mailbox we have just created by changing its permissions.

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

Starting Dovecot

Once we have finished the mailbox creation we will need to make sure the Dovecot application will be run with the server upon restart. We'll use the chkconfig command for that purpose.

sudo chkconfig --level 345 dovecot on

The final step for Dovecot to be completed is to start the service.

sudo service dovecot start

Dovecot should now be up and running.

Postfix Configuration

We now need to go over to the Postfix directories and make the following changes in our main.cf file. The reason for this final piece is so that we can allow our email client to connect to our newly built SMTP server. Exciting stuff!

Please take a moment to navigate over to /etc/postfix/main.cf and open it with your chosen text editor.

sudo nano /etc/postfix/main.cf

Now we should add the following lines.

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

Once you have added the above lines you can exit the main.cf file and restart the Postfix service.

sudo service postfix restart

Iptables port additions

Now that we have enabled secure SMTP 'SSL' we should allow connections to port 587 by opening the port in iptables for our server.  Add the rule for this port by entering the following command:

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

After adding the SSL SMTP port we should also add the POP and IMAP ports along with 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

Once these lines have been added we should save the iptables rules and restart iptables.

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

Summary

In this guide you've learned to configure and install a basic Dovecot setup. The steps you have covered today should have given you a solid foundation of a basic Dovecot install and configuration. From here you can explore the Dovecot package in more depth.

Congratulations

All that is left to do now is to congratulate you on finishing this configuration. With this brief guide you should be on track to a fully-functional mail server.

Thanks for reading!







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