Install Postfix by updating the system and selecting "Internet Site" during setup, entering your domain as the mail name. 2. Configure /etc/postfix/main.cf with correct myhostname, mydomain, inet_interfaces = loopback-only, and mynetworks to restrict relay to localhost. 3. Restart Postfix and test email sending using the mail command after installing mailutils, verifying delivery via /var/log/mail.log. 4. Improve deliverability by setting up SPF DNS records and optionally configuring DKIM with OpenDKIM for email signing. 5. Secure the server by preventing open relay, enabling TLS encryption, monitoring logs, and keeping software updated, ensuring reliable send-only email functionality.

Setting up a Postfix mail server on a Linux system is a practical way to handle email delivery for your domain, whether for application notifications, internal communication, or lightweight email services. While full email hosting (with IMAP/POP3) involves more components, Postfix can be configured as a send-only SMTP server fairly easily. This guide walks you through the essential steps on a typical Ubuntu/Debian system.

1. Install Postfix

Start by updating your system and installing Postfix:

sudo apt update
sudo apt install postfix

During installation, you’ll be prompted to choose a mail server configuration type. For a basic send-only server, select "Internet Site".

You’ll also be asked for the system mail name—this should be your domain (e.g., example.com). Make sure your server’s hostname is properly set and matches DNS records.

If you miss the configuration prompt, run sudo dpkg-reconfigure postfix later.

2. Configure Postfix Settings

The main configuration file is located at /etc/postfix/main.cf. Open it:

sudo nano /etc/postfix/main.cf

Ensure these key parameters are set correctly:

myhostname = mail.example.com
mydomain = example.com
myorigin = $mydomain
inet_interfaces = loopback-only
mydestination = localhost.$mydomain, localhost
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
home_mailbox = Maildir/

• inet_interfaces = loopback-only ensures Postfix only listens locally—this prevents open relay and improves security.
• mynetworks defines trusted networks allowed to relay mail (only localhost here).
• home_mailbox enables local mail delivery to user directories (optional if you're only sending mail externally).

After editing, restart Postfix:

sudo systemctl restart postfix

3. Test Email Sending

Use the mail command to send a test email. Install mailutils (on Debian/Ubuntu) if needed:

sudo apt install mailutils

Send a test message:

echo "This is a test email body" | mail -s "Test Subject" user@example.com

Check the mail log for delivery status:

sudo tail -f /var/log/mail.log

Look for lines indicating successful relay or delivery. If there’s an error, logs will help identify misconfigurations or DNS issues.

4. (Optional) Set Up SPF and DKIM for Deliverability

To avoid emails being marked as spam, configure DNS records:

• SPF Record: Add a TXT record to authorize your server:

  v=spf1 a mx ~all

• DKIM: Consider using opendkim for signing outgoing emails:

  sudo apt install opendkim opendkim-tools

  Then integrate it with Postfix by editing /etc/postfix/main.cf and adding:

  milter_default_action = accept
  milter_protocol = 2
  smtpd_milters = inet:localhost:8891
  non_smtpd_milters = inet:localhost:8891

Generate a DKIM key, publish the public key in DNS, and start the OpenDKIM service.

5. Security and Maintenance Tips

• Avoid Open Relay: Double-check mynetworks and inet_interfaces. An open relay can be exploited for spam.
• Use TLS: Enable encryption by adding to main.cf:

  smtp_use_tls = yes
  smtp_tls_security_level = may

• Monitor Logs: Regularly check /var/log/mail.log for errors or unauthorized access.
• Keep Updated: Apply OS and Postfix updates regularly.

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Setting up a basic Postfix server isn’t complex, but attention to DNS, security, and logging ensures reliable and trusted email delivery. For receiving mail, you’d need additional services like Dovecot, but for sending notifications from scripts or apps, this setup works well.

Basically, get Postfix installed, lock it down to local use, test sending, and secure your DNS records. That’s the core.

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