I will give an example of setting up a simple mail server on Postfix, Dovecot and MySQL.
For the test, I use the Ubuntu 16.04 operating system.
Configure DNS, see my article – How to add MX record
If you named the MX record as mail.example.com, then specify in the /etc/hostname file:
We also specify in the /etc/hosts file (where instead of 192.0.2.2 we specify the external IP address of the server):
127.0.0.1 localhost localhost.localdomain 192.0.2.2 mail.example.com mail
It is advisable to update the system:
sudo apt update sudo apt upgrade sudo reboot
Install certificates, for example, free from Let’s Encrypt as I described in the article:
Installing Certbot in Ubuntu
Install all the necessary components:
sudo apt install postfix postfix-mysql dovecot-core dovecot-imapd dovecot-pop3d dovecot-lmtpd dovecot-mysql mysql-server
During the installation of Postfix, select “Internet Site” and specify the domain, for example example.com (not mail.example.com).
Follow the security recommendations for the database server:
sudo mysql_secure_installation
Connect to the database server:
sudo mysql -u root -p
Let’s create a database, a user and the necessary tables:
CREATE DATABASE mailserver; GRANT SELECT ON mailserver.* TO 'user'@'127.0.0.1' IDENTIFIED BY 'password'; FLUSH PRIVILEGES; USE mailserver; CREATE TABLE `virtual_domains` ( `id` int(11) NOT NULL auto_increment, `name` varchar(50) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE `virtual_users` ( `id` int(11) NOT NULL auto_increment, `domain_id` int(11) NOT NULL, `password` varchar(106) NOT NULL, `email` varchar(100) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `email` (`email`), FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE `virtual_aliases` ( `id` int(11) NOT NULL auto_increment, `domain_id` int(11) NOT NULL, `source` varchar(100) NOT NULL, `destination` varchar(100) NOT NULL, PRIMARY KEY (`id`), FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Fill in the data:
INSERT INTO `mailserver`.`virtual_domains` (`id` ,`name`) VALUES ('1', 'example.com'), ('2', 'mail.example.com'), ('3', 'hostname'), ('4', 'localhost.example.com'); INSERT INTO `mailserver`.`virtual_users` (`id`, `domain_id`, `password` , `email`) VALUES ('1', '1', ENCRYPT('password', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))), 'email1@example.com'), ('2', '1', ENCRYPT('password', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))), 'email2@example.com'); INSERT INTO `mailserver`.`virtual_aliases` (`id`, `domain_id`, `source`, `destination`) VALUES ('1', '1', 'alias@example.com', 'email1@example.com');
Check:
SELECT * FROM mailserver.virtual_domains; SELECT * FROM mailserver.virtual_users; SELECT * FROM mailserver.virtual_aliases; exit
Postfix
Make copies of the standard configuration files and open /etc/postfix/main.cf in any text editor:
sudo mv /etc/postfix/main.cf /etc/postfix/main.cf.orig sudo cp /etc/postfix/master.cf /etc/postfix/master.cf.orig sudo nano /etc/postfix/main.cf
Add settings to it, for example:
#myorigin = /etc/mailname smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) biff = no # appending .domain is the MUA's job. append_dot_mydomain = no # Uncomment the next line to generate "delayed mail" warnings #delay_warning_time = 4h readme_directory = no # TLS parameters smtpd_tls_cert_file=/etc/letsencrypt/live/example.com/fullchain.pem smtpd_tls_key_file=/etc/letsencrypt/live/example.com/privkey.pem smtpd_use_tls=yes smtpd_tls_auth_only = yes smtp_tls_security_level = may smtpd_tls_security_level = may smtpd_sasl_security_options = noanonymous, noplaintext smtpd_sasl_tls_security_options = noanonymous # Authentication smtpd_sasl_type = dovecot smtpd_sasl_path = private/auth smtpd_sasl_auth_enable = yes # Restrictions smtpd_helo_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_non_fqdn_recipient, reject_unknown_recipient_domain, reject_unlisted_recipient, reject_unauth_destination smtpd_sender_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_non_fqdn_sender, reject_unknown_sender_domain smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination myhostname = example.com alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases mydomain = example.com myorigin = $mydomain mydestination = localhost relayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 mailbox_size_limit = 0 recipient_delimiter = + inet_interfaces = all inet_protocols = all # Handing off local delivery to Dovecot's LMTP, and telling it where to store mail virtual_transport = lmtp:unix:private/dovecot-lmtp # Virtual domains, users, and aliases virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf, mysql:/etc/postfix/mysql-virtual-email2email.cf # Even more Restrictions and MTA params disable_vrfy_command = yes strict_rfc821_envelopes = yes #smtpd_etrn_restrictions = reject #smtpd_reject_unlisted_sender = yes #smtpd_reject_unlisted_recipient = yes smtpd_delay_reject = yes smtpd_helo_required = yes smtp_always_send_ehlo = yes #smtpd_hard_error_limit = 1 smtpd_timeout = 30s smtp_helo_timeout = 15s smtp_rcpt_timeout = 15s smtpd_recipient_limit = 40 minimal_backoff_time = 180s maximal_backoff_time = 3h # Reply Rejection Codes invalid_hostname_reject_code = 550 non_fqdn_reject_code = 550 unknown_address_reject_code = 550 unknown_client_reject_code = 550 unknown_hostname_reject_code = 550 unverified_recipient_reject_code = 550 unverified_sender_reject_code = 550
In the file /etc/postfix/mysql-virtual-mailbox-domains.cf add:
user = user password = password hosts = 127.0.0.1 dbname = mailserver query = SELECT 1 FROM virtual_domains WHERE name='%s'
In the file /etc/postfix/mysql-virtual-mailbox-maps.cf add:
user = user password = password hosts = 127.0.0.1 dbname = mailserver query = SELECT 1 FROM virtual_users WHERE email='%s'
In the file /etc/postfix/mysql-virtual-alias-maps.cf add:
user = user password = password hosts = 127.0.0.1 dbname = mailserver query = SELECT destination FROM virtual_aliases WHERE source='%s'
In the file /etc/postfix/mysql-virtual-email2email.cf add:
user = user password = password hosts = 127.0.0.1 dbname = mailserver query = SELECT email FROM virtual_users WHERE email='%s'
In the /etc/postfix/master.cf file, specify:
smtp inet n - n - - smtpd submission inet n - y - - smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_sasl_type=dovecot -o smtpd_sasl_path=private/auth -o smtpd_reject_unlisted_recipient=no -o smtpd_client_restrictions=permit_sasl_authenticated,reject -o milter_macro_daemon_name=ORIGINATING smtps inet n - - - - smtpd -o syslog_name=postfix/smtps -o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yes -o smtpd_sasl_type=dovecot -o smtpd_sasl_path=private/auth -o smtpd_client_restrictions=permit_sasl_authenticated,reject -o milter_macro_daemon_name=ORIGINATING ...
Check the configuration and restart Postfix to apply the changes:
sudo postfix check sudo systemctl restart postfix
Check:
sudo postmap -q example.com mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf sudo postmap -q email1@example.com mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf sudo postmap -q alias@example.com mysql:/etc/postfix/mysql-virtual-alias-maps.cf
Dovecot
We make copies of standard configuration files:
sudo cp /etc/dovecot/dovecot.conf /etc/dovecot/dovecot.conf.orig sudo cp /etc/dovecot/conf.d/10-mail.conf /etc/dovecot/conf.d/10-mail.conf.orig sudo cp /etc/dovecot/conf.d/10-auth.conf /etc/dovecot/conf.d/10-auth.conf.orig sudo cp /etc/dovecot/dovecot-sql.conf.ext /etc/dovecot/dovecot-sql.conf.ext.orig sudo cp /etc/dovecot/conf.d/10-master.conf /etc/dovecot/conf.d/10-master.conf.orig sudo cp /etc/dovecot/conf.d/10-ssl.conf /etc/dovecot/conf.d/10-ssl.conf.orig
Add at the end of /etc/dovecot/dovecot.conf:
## Dovecot configuration file ... # Enable installed protocols !include_try /usr/share/dovecot/protocols.d/*.protocol protocols = imap pop3 lmtp ... postmaster_address=postmaster at example.com
In the file /etc/dovecot/conf.d/10-mail.conf, specify:
... mail_location = maildir:/var/mail/vhosts/%d/%n/ ... mail_privileged_group = mail ...
Create a system user, group and directory for emails:
sudo mkdir -p /var/mail/vhosts/example.com sudo groupadd -g 5000 vmail sudo useradd -g vmail -u 5000 vmail -d /var/mail sudo chown -R vmail:vmail /var/mail
In the file /etc/dovecot/conf.d/10-auth.conf, specify:
... disable_plaintext_auth = yes ... auth_mechanisms = plain login ... !include auth-system.conf.ext ... !include auth-sql.conf.ext ...
In the file /etc/dovecot/conf.d/auth-sql.conf.ext, specify:
... passdb { driver = sql args = /etc/dovecot/dovecot-sql.conf.ext } ... #userdb { # driver = sql # args = /etc/dovecot/dovecot-sql.conf.ext #} ... userdb { driver = static args = uid=vmail gid=vmail home=/var/mail/vhosts/%d/%n } ...
In the file /etc/dovecot/dovecot-sql.conf.ext, specify:
... driver = mysql ... connect = host=127.0.0.1 dbname=mailserver user=user password=password ... default_pass_scheme = SHA512-CRYPT ... password_query = SELECT email as user, password FROM virtual_users WHERE email='%u'; ...
Set the rights:
sudo chown -R vmail:dovecot /etc/dovecot sudo chmod -R o-rwx /etc/dovecot
In the file /etc/dovecot/conf.d/10-master.conf, specify:
... service imap-login { inet_listener imap { #port = 143 } inet_listener imaps { port = 993 ssl = yes } ... } ... service pop3-login { inet_listener pop3 { #port = 110 } inet_listener pop3s { port = 995 ssl = yes } } ...
service lmtp { unix_listener /var/spool/postfix/private/dovecot-lmtp { #mode = 0666i mode = 0600 user = postfix group = postfix } ... }
... service auth { ... unix_listener /var/spool/postfix/private/auth { mode = 0660 user = postfix group = postfix } unix_listener auth-userdb { mode = 0600 user = vmail } ... user = dovecot } ...
... service auth-worker { ... user = vmail }
In the file /etc/dovecot/conf.d/10-ssl.conf, specify:
... # SSL/TLS support: yes, no, required. <doc/wiki/SSL.txt> ssl = required ... ssl_cert = </etc/letsencrypt/live/example.com/fullchain.pem ssl_key = </etc/letsencrypt/live/example.com/privkey.pem
Check the configuration and restart dovecot:
doveconf -n sudo systemctl restart dovecot
Let’s try to send a test letter:
sudo apt-get install mailutils echo "Email body text" | sudo mail -s "Email subject line" username@gmail.com -aFrom:email1@example.com sudo mail -f /var/mail/vhosts/example.com/email1
Make sure Postfix and Dovecot are running:
netstat -na | grep LISTEN | grep 25 netstat -na | grep LISTEN | grep 143 netstat -na | grep LISTEN | grep 587 netstat -na | grep LISTEN | grep 993 netstat -na | grep LISTEN | grep 995
The mail server is configured, you can connect the mail client to the ports: IMAP 143 (STARTTLS, Normal password), 587 (STARTTLS, Normal password).
After installation, you can check the security of the mail server with some services:
https://www.immuniweb.com/ssl/
https://mxtoolbox.com/spf.aspx
https://mxtoolbox.com/DMARC.aspx
See also my articles:
- Installing and Configuring Postfix
- Configuring Spamassassin + Postfix
- Configuring ClamAV + Postfix
- How to enable port 587 in Postfix