Email with Postfix, Dovecot, and MySQL on CentOS 6

The Postfix Mail Transfer Agent (MTA) is a high performance open source e-mail server system. This guide will help you get Postfix running on your CentOS 6 Linode, using Dovecot for IMAP/POP3 service, and MySQL to store information on virtual domains and users.

Note About Email at Linode

This guide may involve or result in sending email. In an effort to fight spam, Linode restricts outbound connections on ports 25, 465, and 587 on all Linodes for new accounts created after November 5th, 2019. For more information, please see Sending Email on Linode.

This guide may involve or result in sending email. In an effort to fight spam, Linode restricts …

Before You Begin

Prior to using this guide, be sure you have followed the Setting Up and Securing a Compute Instance and set your hostname.

Note

The steps in this guide require root privileges. Be sure to run the steps below as root, or use su - root to log in as root. Certain commands below cannot be run as sudo and must be run as root.

Install Required Packages

1. Install any outstanding package updates:

   yum update
   

2. The version of Postfix included in the main CentOS repository does not include support for MySQL; therefore, you will need install Postfix from the CentOS Plus repository. Before doing so, add exclusions to the [base] and [updates] repositories for the Postfix package to prevent it from being overwritten with updates that do not have MySQL support:

   File: /etc/yum.repos.d/CentOS-Base.repo

   1 2 3 4 5 6 7 8

   [base] name=CentOS-$releasever - Base exclude=postfix # released updates [updates] name=CentOS-$releasever - Updates exclude=postfix

3. Install the required packages:

   yum --enablerepo=centosplus install postfix
   yum install dovecot mysql-server dovecot-mysql
   

   This installs the Postfix mail server, the MySQL database server, the Dovecot IMAP and POP daemons, and several supporting packages that provide services related to authentication.

Next, set up a MySQL database to handle virtual domains and users.

Set up MySQL for Virtual Domains and Users

1. Configure MySQL to start on boot, then start MySQL:

   chkconfig mysqld on
   service mysqld start
   

2. Run mysql_secure_installation. You will be presented with the opportunity to change the MySQL root password, remove anonymous user accounts, disable root logins outside of localhost, remove test databases, and reload privilege tables. It is recommended that you answer yes to these options:

   mysql_secure_installation
   

3. Start the MySQL shell:

   mysql -u root -p
   

4. Create a database for your mail server and switch to it:

   CREATE DATABASE mail;
   USE mail;
   

5. Create a mail administration user called mail_admin and grant it permissions on the mail database. Please be sure to replace mail_admin_password with a strong password:

   GRANT SELECT, INSERT, UPDATE, DELETE ON mail.* TO 'mail_admin'@'localhost' IDENTIFIED BY 'mail_admin_password';
   GRANT SELECT, INSERT, UPDATE, DELETE ON mail.* TO 'mail_admin'@'localhost.localdomain' IDENTIFIED BY 'mail_admin_password';
   FLUSH PRIVILEGES;
   

6. Create the virtual domains table:

   CREATE TABLE domains (domain varchar(50) NOT NULL, PRIMARY KEY (domain) );
   

7. Create a table to handle mail forwarding:

   CREATE TABLE forwardings (source varchar(80) NOT NULL, destination TEXT NOT NULL, PRIMARY KEY (source) );
   

8. Create the users table:

   CREATE TABLE users (email varchar(80) NOT NULL, password varchar(20) NOT NULL, PRIMARY KEY (email) );
   

9. Create a transports table:

   CREATE TABLE transport ( domain varchar(128) NOT NULL default '', transport varchar(128) NOT NULL default '', UNIQUE KEY domain (domain) );
   

10. Exit the MySQL shell:

    quit
    

11. Bind MySQL to localhost (127.0.0.1) by editing /etc/my.cnf, and adding the following to the [mysqld] section of the file:

    File: /etc/my.cnf

    1	bind-address=127.0.0.1

    This is required for Postfix to be able to communicate with the database server. If you have MySQL set up to listen on another IP address (such as an internal IP), you will need to substitute this IP address in place of 127.0.0.1 during the Postfix configuration steps. It is not advisable to run MySQL on a publicly-accessible IP address.

12. Restart the database server:

    service mysqld restart
    

Next, perform additional Postfix configuration to set up communication with the database.

Configure Postfix to work with MySQL

Note

For the next four steps, replace mail_admin_password with the mail_admin password input earlier.

1. Create a virtual domain configuration file for Postfix called /etc/postfix/mysql-virtual_domains.cf:

   File: /etc/postfix/mysql-virtual_domains.cf

   1 2 3 4 5

   user = mail_admin password = mail_admin_password dbname = mail query = SELECT domain AS virtual FROM domains WHERE domain='%s' hosts = 127.0.0.1

2. Create a virtual forwarding file for Postfix called /etc/postfix/mysql-virtual_forwardings.cf:

   File: /etc/postfix/mysql-virtual_forwardings.cf

   1 2 3 4 5

   user = mail_admin password = mail_admin_password dbname = mail query = SELECT destination FROM forwardings WHERE source='%s' hosts = 127.0.0.1

3. Create a virtual mailbox configuration file for Postfix called /etc/postfix/mysql-virtual_mailboxes.cf:

   File: /etc/postfix/mysql-virtual_mailboxes.cf

   1 2 3 4 5

   user = mail_admin password = mail_admin_password dbname = mail query = SELECT CONCAT(SUBSTRING_INDEX(email,<'@'>,-1),'/',SUBSTRING_INDEX(email,<'@'>,1),'/') FROM users WHERE email='%s' hosts = 127.0.0.1

4. Create a virtual email mapping file for Postfix called /etc/postfix/mysql-virtual_email2email.cf:

   File: /etc/postfix/mysql-virtual_email2email.cf

   1 2 3 4 5

   user = mail_admin password = mail_admin_password dbname = mail query = SELECT email FROM users WHERE email='%s' hosts = 127.0.0.1

5. Set proper permissions and ownership for these configuration files:

   chmod o= /etc/postfix/mysql-virtual_*.cf
   chgrp postfix /etc/postfix/mysql-virtual_*.cf
   

6. Create a user and group for mail handling. All virtual mailboxes will be stored under this user’s home directory:

   groupadd -g 5000 vmail
   useradd -g vmail -u 5000 vmail -d /home/vmail -m
   

7. Complete the remaining steps required for Postfix configuration. Please be sure to replace server.example.com with the Linode’s fully qualified domain name. If you are planning on using your own SSL certificate and key, replace /etc/pki/dovecot/private/dovecot.pem with the appropriate path:

   postconf -e 'myhostname = server.example.com'
   postconf -e 'mydestination = $myhostname, localhost, localhost.localdomain'
   postconf -e 'mynetworks = 127.0.0.0/8'
   postconf -e 'inet_interfaces = all'
   postconf -e 'message_size_limit = 30720000'
   postconf -e 'virtual_alias_domains ='
   postconf -e 'virtual_alias_maps = proxy:mysql:/etc/postfix/mysql-virtual_forwardings.cf, mysql:/etc/postfix/mysql-virtual_email2email.cf'
   postconf -e 'virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql-virtual_domains.cf'
   postconf -e 'virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql-virtual_mailboxes.cf'
   postconf -e 'virtual_mailbox_base = /home/vmail'
   postconf -e 'virtual_uid_maps = static:5000'
   postconf -e 'virtual_gid_maps = static:5000'
   postconf -e 'smtpd_sasl_type = dovecot'
   postconf -e 'smtpd_sasl_path = private/auth'
   postconf -e 'smtpd_sasl_auth_enable = yes'
   postconf -e 'broken_sasl_auth_clients = yes'
   postconf -e 'smtpd_sasl_authenticated_header = yes'
   postconf -e 'smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination'
   postconf -e 'smtpd_use_tls = yes'
   postconf -e 'smtpd_tls_cert_file = </etc/pki/dovecot/certs/dovecot.pem'
   postconf -e 'smtpd_tls_key_file = </etc/pki/dovecot/private/dovecot.pem'
   postconf -e 'virtual_create_maildirsize = yes'
   postconf -e 'virtual_maildir_extended = yes'
   postconf -e 'proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $relay_domains $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $transport_maps $mynetworks $virtual_mailbox_limit_maps'
   postconf -e 'virtual_transport = dovecot'
   postconf -e 'dovecot_destination_recipient_limit = 1'
   

8. Edit the file /etc/postfix/master.cf and add the Dovecot service to the bottom of the file:

   File: /etc/postfix/master.cf

   1 2	dovecot unix - n n - - pipe flags=DRhu user=vmail:vmail argv=/usr/libexec/dovecot/deliver -f ${sender} -d ${recipient}

9. Configure Postfix to start on boot and start the service for the first time:

   chkconfig postfix on
   service postfix start
   

This completes the configuration for Postfix.

Configure Dovecot

1. Move /etc/dovecot/dovecot.conf to a backup file:

   mv /etc/dovecot/dovecot.conf /etc/dovecot/dovecot.conf-backup
   

2. Copy the following into the now-empty dovecot.conf file, substituting your system’s domain name for example.com in line 37:

   File: /etc/dovecot/dovecot.conf

   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

   protocols = imap pop3 log_timestamp = "%Y-%m-%d %H:%M:%S " mail_location = maildir:/home/vmail/%d/%n/Maildir ssl_cert = </etc/pki/dovecot/certs/dovecot.pem ssl_key = </etc/pki/dovecot/private/dovecot.pem namespace { type = private separator = . prefix = INBOX. inbox = yes } service auth { unix_listener auth-master { mode = 0600 user = vmail } unix_listener /var/spool/postfix/private/auth { mode = 0666 user = postfix group = postfix } user = root } service auth-worker { user = root } protocol lda { log_path = /home/vmail/dovecot-deliver.log auth_socket_path = /var/run/dovecot/auth-master postmaster_address = postmaster@example.com } protocol pop3 { pop3_uidl_format = %08Xu%08Xv } passdb { driver = sql args = /etc/dovecot/dovecot-sql.conf.ext } userdb { driver = static args = uid=5000 gid=5000 home=/home/vmail/%d/%n allow_all_users=yes }

3. MySQL will be used to store password information, so /etc/dovecot/dovecot-sql.conf.ext must be created. Insert the following contents into the file, making sure to replace mail_admin_password with your mail password:

   File: /etc/dovecot/dovecot-sql.conf.ext

   1 2 3 4

   driver = mysql connect = host=127.0.0.1 dbname=mail user=mail_admin password=mail_admin_password default_pass_scheme = CRYPT password_query = SELECT email as user, password FROM users WHERE email='%u';

4. Restrict access to the file by changing the permissions to allow users in the dovecot group to access it, while denying access to others:

   chgrp dovecot /etc/dovecot/dovecot-sql.conf.ext
   chmod o= /etc/dovecot/dovecot-sql.conf.ext
   

5. Configure Dovecot to start on boot, and start it for the first time:

   chkconfig dovecot on
   service dovecot start
   

6. Check /var/log/maillog to make sure Dovecot started without errors. Your log should have lines similar to the following:

   File: /var/log/maillog

   1 2 3

   Mar 18 15:21:59 sothoryos postfix/postfix-script[3069]: starting the Postfix mail system Mar 18 15:22:00 sothoryos postfix/master[3070]: daemon started -- version 2.6.6, configuration /etc/postfix Mar 18 15:32:03 sothoryos dovecot: master: Dovecot v2.0.9 starting up (core dumps disabled)

7. Test your POP3 server to make sure it’s running properly:

   yum install telnet
   telnet localhost pop3
   

8. The terminal should output results similar to the following:

   Trying 127.0.0.1...
   Connected to localhost.localdomain.
   Escape character is '^]'.
   +OK Dovecot ready.
   

9. Enter the command quit to return to your shell. This completes the Dovecot configuration. Next, you’ll make sure aliases are configured properly.

Configure Mail Aliases

1. Edit the file /etc/aliases, making sure the postmaster and root directives are set properly for your organization:

   File: /etc/aliases

   1 2	postmaster: root root: postmaster@example.com

2. Update aliases and restart Postfix:

   newaliases
   service postfix restart
   

This completes alias configuration. Next, test Postfix to make sure it’s operating properly.

Testing Postfix

1. Test Postfix for SMTP-AUTH and TLS:

   telnet localhost 25
   

2. While still connected, issue the following command:

   ehlo localhost
   

3. You should see output similar to the following:

   250-hostname.example.com
   250-PIPELINING
   250-SIZE 30720000
   250-VRFY
   250-ETRN
   250-STARTTLS
   250-AUTH PLAIN
   250-AUTH=PLAIN
   250-ENHANCEDSTATUSCODES
   250-8BITMIME
   250 DSN
   

4. Issue the command quit to terminate the telnet connection.

Next, populate the MySQL database with domains and email users.

Set Up and Test Domains and Users

Note

Before continuing, modify the DNS records for any domains that you wish to handle email by adding an MX record that points to your mail server’s fully qualified domain name. If MX records already exist for a domain you would like to handle the email for, either delete them or set them to a higher priority number than your mail server. Smaller priority numbers indicate higher priority for mail delivery, with “0” being the highest priority.

In the following example, the MySQL shell is used to add support for the domain “example.com”, which will have an email account called “sales”.

1. Log into the MySQL shell:

   mysql -u root -p
   

2. Switch to the mail database, add support for your domain, and create an email account. Be sure to replace example.com with your domain name, sales@example.com with your chosen email, and password with a strong password:

   USE mail;
   INSERT INTO domains (domain) VALUES ('example.com');
   INSERT INTO users (email, password) VALUES ('sales@example.com', ENCRYPT('password'));
   quit
   

3. Prior to accessing any newly-created email account, a test message needs to be sent to create that user’s mailbox:

   yum install mailx
   mailx sales@example.com
   

   Press Ctrl+D to complete the message. You can safely leave the field for Cc: blank. This completes the configuration for a new domain and email user.

Note

Given the possibility for virtual hosting a large number of domains on a single mail system, the username portion of an email address (i.e. before the @ sign) is not sufficient for authentication. When email users authenticate to the server, they must supply the entire email address created above as their username.

Check Your Logs

After the test mail is sent, check the mail logs to make sure the mail was delivered.

1. Check the maillog located in /var/log/maillog. You should see something similar to the following:

   File: /var/log/maillog

   1 2 3 4

   Mar 18 15:39:07 server postfix/cleanup[3252]: 444E34055: message-id=<20150318153907.444E34055@server.example.com> Mar 18 15:39:07 server postfix/qmgr[3218]: 444E34055: from=<root@server.example.com>, size=489, nrcpt=1 (queue active) Mar 18 15:39:07 server postfix/pipe[3258]: 444E34055: to=<sales@example.com>, relay=dovecot, delay=0.09, delays=0.04/0.01/0/0.05, dsn=2.0.0, sta$ Mar 18 15:39:07 server postfix/qmgr[3218]: 444E34055: removed

2. Check the Dovecot delivery log located in /home/vmail/dovecot-deliver.log. The contents should look similar to the following:

   File: /home/vmail/dovecot-deliver.log

   1	deliver(<sales@example.com>): 2011-01-21 20:03:19 Info: msgid=\<<20110121200319.E1D148908@hostname.example.com>>: saved mail to INBOX

Now you can test to see what the users of your email server would see with their email clients.

Test the Mailbox

1. To test the sales@example.com mailbox, navigate to the mailbox directory /home/vmail/example.com/sales/Maildir and issue the following command:

   cd /home/vmail/example.com/sales/Maildir
   find
   

2. You should see output similar to the following:

   .
   ./dovecot-uidlist
   ./cur
   ./new
   ./new/1285609582.P6115Q0M368794.li172-137
   ./dovecot.index
   ./dovecot.index.log
   ./tmp
   

3. Test the mailbox by using a mail client. For this test, using mutt is recommended. If it is not installed by default, install it with yum install mutt, then run:

   mutt -f .
   

   You may be prompted to create the root mailbox. This is not required.

4. If there is an email in the inbox, Postfix, Dovecot, and MySQL have been successfully configured! To quit mutt press q.

   

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

• ISP-style Email Server with Debian-Lenny and Postfix 2.5 guide
• Groupware Server With Group-Office, Postfix, Dovecot And SpamAssassin On Debian Lenny (5.0)
• Postfix MySQL Howto
• Postfix SASL Howto
• Dovecot Documentation Wiki
• MySQL Documentation