Setting up a secure mail server on Ubuntu 22.04 LTS (Jammy Jellyfish)

In this tutorial you will learn how to configure a mail server that uses Postfix, Dovecot, Rspamd, DKIM, and MariaDB to deliver mails securely. You learn also how to install a Roundcube webmail interface to be able to read your emails directly from your browser.

Before you start

To complete the actions presented below, you must have:

• A Scaleway account logged into the console
• Owner status or IAM permissions allowing you to perform actions in the intended Organization
• An SSH key
• An Instance running Ubuntu 24.04 or later
• A domain or subdomain configured to point to the IP address of your Instance
• Enabled the SMTP ports to send emails from your Instance

Pre-work and system preparation

1. Update the system:

   apt update && apt upgrade -y

2. Ensure no conflicting mail software is installed:

   service sendmail stop
   update-rc.d -f sendmail remove

   Note

   If the message Failed to stop sendmail.service appears, it can be safely ignored.

Install Nginx, PHP, and MariaDB

1. Install the required packages:

   apt install nginx mariadb-server php-fpm php-cli php-imap php-json php-mysql php-opcache php-mbstring php-readline php-intl -y

2. Secure the MariaDB installation:

   mysql_secure_installation

   During the setup, provide answers to secure your MariaDB installation (set the root password, remove anonymous users, disallow remote root login, etc.). Refer to Installing and Securing MariaDB for further details regarding the configuration of MariaDB.

Install and configure PostfixAdmin

1. Download and extract PostfixAdmin.

   wget -O postfixadmin.tgz https://github.com/postfixadmin/postfixadmin/archive/postfixadmin-3.3.15.tar.gz
   tar -zxvf postfixadmin.tgz
   mv postfixadmin-postfixadmin-3.3.15/ /var/www/postfixadmin

   Note

   In this tutorial we are using version 3.3.15. Refer to the official PostFixAdmin repository to check the latest stable version.

2. Set the correct file permissions:

   chown -R www-data: /var/www/postfixadmin

3. Log into MariaDB using the root user:

   mysql -u root -p

   Run the following SQL commands to create a MariaDB database for PostfixAdmin:

   CREATE DATABASE postfixadmin;
   GRANT ALL ON postfixadmin.* TO 'postfixadmin'@'localhost' IDENTIFIED BY 'your_secret_password';
   FLUSH PRIVILEGES;
   EXIT;

4. Create the PostfixAdmin configuration file:

   nano /var/www/postfixadmin/config.local.php

   Add the following content:

   <?php
   $CONF['configured'] = true;
   $CONF['database_type'] = 'mysqli';
   $CONF['database_host'] = 'localhost';
   $CONF['database_user'] = 'postfixadmin';
   $CONF['database_password'] = 'your_secret_password';
   $CONF['database_name'] = 'postfixadmin';
   ?>

5. Initialize the PostfixAdmin database schema:

   sudo -u www-data php /var/www/postfixadmin/public/upgrade.php

6. Create an admin user for PostfixAdmin:

   bash /var/www/postfixadmin/scripts/postfixadmin-cli admin add

   Follow the prompts to add your email address and create the admin user.

7. Create an Nginx configuration file for PostfixAdmin::

   nano /etc/nginx/sites-available/mail.example.com.conf

   Add the following configuration:

   server {
       listen 80;
       server_name mail.example.com;
       root /var/www;
   
       location / {
           try_files $uri $uri/ /index.php;
       }
   
       location /postfixadmin {
           index index.php;
           try_files $uri $uri/ /postfixadmin/public/login.php;
       }
   
       location ~ \.php$ {
           fastcgi_pass unix:/run/php/php*-fpm.sock;
           fastcgi_index index.php;
           include fastcgi_params;
           fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
       }
   }

8. Activate the Nginx configuration and reload:

   ln -s /etc/nginx/sites-available/mail.example.com.conf /etc/nginx/sites-enabled/
   systemctl reload nginx

Generate and apply a Let's Encrypt TLS/SSL certificate

1. Install Certbot for Nginx:

   apt install certbot python3-certbot-nginx -y

2. Run the following command to generate a Let's Encrypt TLS/SSL certificate for your mail domain:

   certbot --nginx -d mail.example.com

   Follow the prompts to enter your email, agree to terms, and choose HTTPS options. Certbot will automatically configure SSL for Nginx and restart the service.

3. Visit https://mail.example.com to ensure your website is now accessible via HTTPS with the TLS/SSL certificate applied.

Install and configure Postfix and Dovecot

1. Install Postfix, Dovecot, and necessary packages:

   apt install postfix postfix-mysql dovecot-imapd dovecot-lmtpd dovecot-pop3d dovecot-mysql -y

2. After installing Postfix, update its configuration to use the Let's Encrypt certificate:

   postconf -e 'smtpd_tls_cert_file=/etc/letsencrypt/live/mail.example.com/fullchain.pem'
   postconf -e 'smtpd_tls_key_file=/etc/letsencrypt/live/mail.example.com/privkey.pem'
   postconf -e 'smtpd_use_tls=yes'
   postconf -e 'smtpd_tls_security_level=may'
   postconf -e 'smtp_tls_security_level=may'

3. Configure Dovecot to use the SSL certificate: Edit the file /etc/dovecot/conf.d/10-ssl.conf:

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

   Update the SSL settings:

   ssl = yes
   ssl_cert = </etc/letsencrypt/live/mail.example.com/fullchain.pem
   ssl_key = </etc/letsencrypt/live/mail.example.com/privkey.pem
   ssl_dh = </etc/ssl/certs/dhparam.pem
   ssl_cipher_list = EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH
   ssl_prefer_server_ciphers = yes

4. Restart Dovecot to apply the changes:

   systemctl restart dovecot

Configure DKIM with Rspamd

1. Install Redis and Rspamd:

   apt install redis-server rspamd -y

2. Generate DKIM keys and configure Rspamd for signing:

   mkdir /var/lib/rspamd/dkim/
   rspamadm dkim_keygen -b 2048 -s mail -k /var/lib/rspamd/dkim/mail.key > /var/lib/rspamd/dkim/mail.pub

3. Add DKIM signing configuration by opening the file /etc/rspamd/local.d/dkim_signing.conf in a text editor:

   nano /etc/rspamd/local.d/dkim_signing.conf

   Then add the following content:

   selector = "mail";
   path = "/var/lib/rspamd/dkim/$selector.key";
   allow_username_mismatch = true;

4. Restart Rspamd to apply the configuration:

   systemctl restart rspamd

5. Retrieve the DKIM public key for your domain:

   cat /var/lib/rspamd/dkim/mail.pub

   Add the output as a TXT record to your domain's DNS zone to publish your DKIM public key in DNS. Refer to How to manage DNS records for furher information.

Install Roundcube Webmail

1. Install the PHP dependencies for Roundcube:

   apt install php-intl php-mail-mime php-net-smtp php-net-socket php-pear php-xml php-intl php-gd php-imagick -y

2. Log into MariaDB using the root user:

   mysql -u root -p

   Execute the following SQL commands to create a MariaDB database for Roundcube:

   CREATE DATABASE roundcubemail;
   GRANT ALL ON roundcubemail.* TO 'roundcube'@'localhost' IDENTIFIED BY 'your_secret_password';
   FLUSH PRIVILEGES;
   EXIT;

3. Download and install Roundcube:

   wget https://github.com/roundcube/roundcubemail/releases/download/1.6.1/roundcubemail-1.6.1-complete.tar.gz
   tar xzf roundcubemail-1.6.1-complete.tar.gz
   mv roundcubemail-1.6.1 /var/www/webmail
   chown -R www-data: /var/www/webmail

4. Edit the Nginx configuration file (/etc/nginx/sites-enabled/mail.example.com.conf):

   nano /etc/nginx/sites-enabled/mail.example.com.conf

   And add the following section for Roundcube:

   location /webmail {
       index index.php;
       try_files $uri $uri/ /webmail/index.php;
   }

5. Restart Nginx to apply changes:

   systemctl restart nginx

6. Complete the Roundcube setup by visiting https://mail.example.com/webmail/installer/ and following the web-based setup.

7. Remove the installer directory for security:

   rm -rf /var/www/webmail/installer

Automate SSL renewal with Certbot

Let's Encrypt certificates have a limited validity. Ensure the SSL certificates renew automatically:

certbot renew --dry-run