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How To Configure a Mail Server on Linux


How To: Configure a Mail Server

Before setting up your mail server, it’s necessary your VPS has the following:

  • Domain is forwarding to your server (setup domain)
  • MySQL installed and configured (setup mysql)
  • User with root privileges (setup new users- omit step 5)
  • Configure and identify your FQDN (setup FQDN)

Optional: SSL certificate (setup free signed ssl certificate)

Install Packages

apt-get install postfix postfix-mysql dovecot-core dovecot-imapd dovecot-lmtpd dovecot-mysql

When Postfix configuration is prompted choose Internet Site:

Create a MySQL Database, Virtual Domains, Users and Aliases

After the installation finishes, we are going to create a MySQL database to configure three different tables: one for domains, one for users and the last one for aliases.

We are going to name the database servermail, but you can use whatever name you want.

Create the servermail database:

mysqladmin -p create servermail

Log in as MySQL root user

mysql -u root -p

Enter your MySQL root’s password; if it’s successful you will see:

mysql >

First we need to create a new user, specific for mail authentication, and we are going to give SELECT permission.

mysql > GRANT SELECT ON servermail.* TO 'usermail'@'' IDENTIFIED BY 'mailpassword';

After that, we need to reload MySQL privileges to ensure it applies those permissions successfully:


Finally we need to use the database for creating tables and introduce our data:

mysql> USE servermail;

We are going to create a table for the specific domains recognized as authorized domains.

CREATE TABLE `virtual_domains` (
`name` VARCHAR(50) NOT NULL,

We are going to create a table to introduce the users. Here you will add the email address and passwords. It is necessary to associate each user with a domain.

CREATE TABLE `virtual_users` (
`domain_id` INT NOT NULL,
`password` VARCHAR(106) NOT NULL,
`email` VARCHAR(120) NOT NULL,
UNIQUE KEY `email` (`email`),
FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE

Finally we are going to create a virtual aliases table to specify all the emails that you are going to forward to the other email.

CREATE TABLE `virtual_aliases` (
`domain_id` INT NOT NULL,
`source` varchar(100) NOT NULL,
`destination` varchar(100) NOT NULL,
FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE

We have created the three tables successfully. Now we are going to introduce the data.


Here we are going to introduce your domains inside the virtual_domains table. You can add all the domains you want, but in this tutorial we are going to introduce just the primary domain ( and your FQDN (

INSERT INTO `servermail`.`virtual_domains`
(`id` ,`name`)
('1', ''),
('2', '');


We are going to introduce the email address and passwords associated for each domain. Make sure you change all the info with your specific information.

INSERT INTO `servermail`.`virtual_users`
(`id`, `domain_id`, `password` , `email`)
('1', '1', ENCRYPT('firstpassword', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))), ''),
('2', '1', ENCRYPT('secondpassword', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))), '');


We are going to introduce the email address (source) that we are going to forward to the other email address (destination).

INSERT INTO `servermail`.`virtual_aliases`
(`id`, `domain_id`, `source`, `destination`)
('1', '1', '', '');

Exit MySQL

 mysql > exit

Configure Postfix

We are going to configure Postfix to handle the SMTP connections and send the messages for each user introduced in the MySQL Database.

First we need to create a copy of the default file, in case you want to revert to the default configuration.

cp /etc/postfix/ /etc/postfix/

Open the file to modify it:

nano /etc/postfix/

First we need to comment the TLS Parameters and append other parameters. In this tutorial, we are using the Free SSL certificates and the paths that are suggested in the tutorial (link), but you could modify depending your personal configurations.

# TLS parameters
#smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
#smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache 
smtpd_tls_auth_only = yes

Then we are going to append the following parameters below the TLS settings that we have changed in the previous step:

smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
smtpd_recipient_restrictions =

We need to comment the mydestination default settings and replace it with localhost. This change allows your VPS to use the virtual domains inside the MySQL table.

#mydestination =,,, localhost
mydestination = localhost 

Verify that myhostname parameter is set with your FQDN.

myhostname =

Append the following line for local mail delivery to all virtual domains listed inside the MySQL table.

virtual_transport = lmtp:unix:private/dovecot-lmtp

Finally, we need to add these three parameters to tell Postfix to configure the virtual domains, users and aliases.

virtual_mailbox_domains = mysql:/etc/postfix/
virtual_mailbox_maps = mysql:/etc/postfix/
virtual_alias_maps = mysql:/etc/postfix/

We are going to create the final three files that we append in the file to tell Postfix how to connect with MySQL.

First we need to create the file. It’s necessary to change the values depending your personal configuration.

nano /etc/postfix/
user = usermail
password = mailpassword
hosts =
dbname = servermail
query = SELECT 1 FROM virtual_domains WHERE name='%s'

Then we need to restart Postfix.

service postfix restart

We need to ensure that Postfix finds your domain, so we need to test it with the following command. If it is successful, it should returns 1:

postmap -q mysql:/etc/postfix/

Then we need to create the file.

nano /etc/postfix/ 
user = usermail
password = mailpassword
hosts =
dbname = servermail
query = SELECT 1 FROM virtual_users WHERE email='%s'

We need to restart Postfix again.

service postfix restart

At this moment we are going to ensure Postfix finds your first email address with the following command. It should return 1 if it’s successful:

postmap -q mysql:/etc/postfix/

Finally, we are going to create the last file to configure the connection between Postfix and MySQL.

nano /etc/postfix/
user = usermail
password = mailpassword
hosts =
dbname = servermail
query = SELECT destination FROM virtual_aliases WHERE source='%s'

Restart Postfix

service postfix restart

We need to verify Postfix can find your aliases. Enter the following command and it should return the mail that’s forwarded to the alias:

postmap -q mysql:/etc/postfix/

If you want to enable port 587 to connect securely with email clients, it is necessary to modify the /etc/postfix/ file

nano /etc/postfix/

We need to uncomment these lines and append other parameters:

submission inet n       -       -       -       -       smtpd
-o syslog_name=postfix/submission
-o smtpd_tls_security_level=encrypt
-o smtpd_sasl_auth_enable=yes
-o smtpd_client_restrictions=permit_sasl_authenticated,reject

In some cases, we need to restart Postfix to ensure port 587 is open.

service postfix restart

Note: You can use this tool to scan your domain ports and verify that port 25 and 587 are open (

Configure Dovecot

We are going to copy the 7 files we’re going to modify, so that you could revert it to default if you needed to. Enter the following commands one by one:

cp /etc/dovecot/dovecot.conf /etc/dovecot/dovecot.conf.orig
cp /etc/dovecot/conf.d/10-mail.conf /etc/dovecot/conf.d/10-mail.conf.orig
cp /etc/dovecot/conf.d/10-auth.conf /etc/dovecot/conf.d/10-auth.conf.orig
cp /etc/dovecot/dovecot-sql.conf.ext /etc/dovecot/dovecot-sql.conf.ext.orig
cp /etc/dovecot/conf.d/10-master.conf /etc/dovecot/conf.d/10-master.conf.orig
cp /etc/dovecot/conf.d/10-ssl.conf /etc/dovecot/conf.d/10-ssl.conf.orig

Edit configuration file from Dovecot.

nano /etc/dovecot/dovecot.conf

Verify this option is uncommented.

!include conf.d/*.conf

We are going to enable protocols (add pop3 if you want to) below the !include_try /usr/share/dovecot/protocols.d/*.protocol line.

!include_try /usr/share/dovecot/protocols.d/*.protocol
protocols = imap lmtp

Then we are going to edit the mail configuration file:

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

Find the mail_location line, uncomment it, and put the following parameter:

mail_location = maildir:/var/mail/vhosts/%d/%n

Find the mail_privileged_group line, uncomment it, and add the mail parameter like so:

mail_privileged_group = mail


Enter this command:

ls -ld /var/mail

Ensure permissions are like this:

>drwxrwsr-x 3 root vmail 4096 Jan 24 21:23 /var/mail

We are going to create a folder for each domain that we register in the MySQL table:

mkdir -p /var/mail/vhosts/

Create a vmail user and group with an id of 5000

groupadd -g 5000 vmail 
useradd -g vmail -u 5000 vmail -d /var/mail

We need to change the owner of the /var/mail folder to the vmail user.

chown -R vmail:vmail /var/mail

Then we need to edit the /etc/dovecot/conf.d/10-auth.conf file:

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

Uncomment plain text authentication and add this line:

disable_plaintext_auth = yes

Modify auth_mechanisms parameter:

auth_mechanisms = plain login

Comment this line:

#!include auth-system.conf.ext

Enable MySQL authorization by uncommenting this line:

!include auth-sql.conf.ext

We need to create the /etc/dovecot/dovecot-sql.conf.ext file with your information for authentication:

nano /etc/dovecot/conf.d/auth-sql.conf.ext

Enter the following code in the file:

passdb {
  driver = sql
  args = /etc/dovecot/dovecot-sql.conf.ext
userdb {
  driver = static
  args = uid=vmail gid=vmail home=/var/mail/vhosts/%d/%n

We need to modify the /etc/dovecot/dovecot-sql.conf.ext file with our custom MySQL information:

nano /etc/dovecot/dovecot-sql.conf.ext

Uncomment the driver parameter and set mysql as parameter:

driver = mysql

Uncomment the connect line and introduce your MySQL specific information:

connect = host= dbname=servermail user=usermail password=mailpassword

Uncomment the default_pass_scheme line and change it to SHA-512.

default_pass_scheme = SHA512-CRYPT

Uncomment the >password_query line and add this information:

password_query = SELECT email as user, password FROM virtual_users WHERE email='%u';

Change the owner and the group of the dovecot folder to vmail user:

chown -R vmail:dovecot /etc/dovecot
chmod -R o-rwx /etc/dovecot 

Open and modify the /etc/dovecot/conf.d/10-master.conf file (be careful because different parameters will be changed).

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

##Uncomment inet_listener_imap and modify to port 0
service imap-login {
  inet_listener imap {
    port = 0

#Create LMTP socket and this configurations
service lmtp {
   unix_listener /var/spool/postfix/private/dovecot-lmtp {
       mode = 0600
       user = postfix
       group = postfix
  #inet_listener lmtp {
    # Avoid making LMTP visible for the entire internet
    #address =
    #port =

Modify unix_listener parameter to service_auth like this:

service auth {

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

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

  #unix_listener /var/spool/postfix/private/auth {
  # mode = 0666

  user = dovecot

Modify service auth-worker like this:

service auth-worker {
  # Auth worker process is run as root by default, so that it can access
  # /etc/shadow. If this isn't necessary, the user should be changed to
  # $default_internal_user.
  user = vmail

Finally, we are going to modify the SSL configuration file from Dovecot (skip this step if you are going to use default configuration).

# nano /etc/dovecot/conf.d/10-ssl.conf

Change the ssl parameter to required:

ssl = required

And modify the path for ssl_cert and ssl_key:

ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem

Restart Dovecot

service dovecot restart

You should check that port 993 is open and working (in case you enable pop3; you should check also port 995).

telnet 993

Congratulations. You have successfully configured your mail server and you may test your account using an email client:

- Username:
- Password: email1's password

Note: use port 993 for secure IMAP and port 587 or 25 for SMTP.

Configure SpamAssassin

First we need to install SpamAssassin.

apt-get install spamassassin spamc

Then we need to create a user for SpamAssassin.

adduser spamd --disabled-login

To successfully configure SpamAssassin, it’s necessary to open and modify the configuration settings.

nano /etc/default/spamassassin

We need to change the ENABLED parameter to enable SpamAssassin daemon.


We need to configure the home and options parameters.

OPTIONS="--create-prefs --max-children 5 --username spamd --helper-home-dir ${SPAMD_HOME} -s ${SPAMD_HOME}spamd.log" 

Then we need to specify the PID_File parameter like this:


Finally, we need to specify that SpamAssassin’s rules will be updated automatically.


We need to open /etc/spamassassin/ to set up the anti-spam rules.

nano /etc/spamassassin/

SpamAssassin will score each mail and if it determines this email is greater than 5.0 on its spam check, then it automatically will be considered spam. You could use the following parameters to configure the anti-spam rules:

rewrite_header Subject ***** SPAM _SCORE_ *****
report_safe             0
required_score          5.0
use_bayes               1
use_bayes_rules         1
bayes_auto_learn        1
skip_rbl_checks         0
use_razor2              0
use_dcc                 0
use_pyzor               0

We need to change the Postfix /etc/postfix/ file to tell it that each email will be checked with SpamAssassin.

nano /etc/postfix/

Then we need to find the following line and add the spamassassin filter:

smtp      inet  n       -       -       -       -       smtpd
-o content_filter=spamassassin

Finally we need to append the following parameters:

spamassassin unix -     n       n       -       -       pipe
user=spamd argv=/usr/bin/spamc -f -e  
/usr/sbin/sendmail -oi -f ${sender} ${recipient}

It is necessary to start SpamAssassin and restart Postfix to begin verifying spam from emails.

service spamassassin start
service postfix restart

Congratulations! You have successfully set up your mail server with Postfix and Dovecot with MySQL authentication and spam filtering with SpamAssassin!

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