How to Configure SMTP Server to Send Mail in Linux

How to Configure an SMTP Server to Send Mail in Linux

Setting up an SMTP server on a Linux machine can seem daunting, but with the proper guidance, it becomes straightforward. SMTP (Simple Mail Transfer Protocol) is essential for sending emails over the Internet. This guide will walk you through the steps needed to configure an SMTP server reliably.

Step 1: Choose an SMTP Server Software

There are several SMTP server software options available for Linux. Among the most popular ones are:

• Postfix
• Sendmail
• Exim

Each of these mail transfer agents (MTAs) has its unique features; for most users, Postfix is an excellent choice due to its simplicity and security features.

Step 2: Install Your Chosen SMTP Server

To install Postfix, for example, you can use the following command:

sudo apt-get install postfix

During the installation, you’ll be prompted to choose the type of mail configuration. Select "Internet Site" and set your system’s mail name to match your domain name.

Step 3: Configure the SMTP Server

Post-installation, you'll need to configure the main settings. The configuration file is usually located at /etc/postfix/main.cf. Here are crucial settings to consider:

1. myhostname: Define your server’s hostname.
2. mydomain: Specify your domain.
3. mydestination: Identify domains that will be delivered locally.

Step 4: Set Up Authentication and Security

Securing your email server with SASL authentication is vital. You can configure SASL by adding the following lines to your main.cf:

smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

Then create the sasl_passwd file, which should contain your SMTP credentials:

[smtp.yourserver.com]:USERNAME:PASSWORD

Remember to set appropriate permissions for this file:

sudo chmod 600 /etc/postfix/sasl_passwd

Step 5: Restart the SMTP Service

After making changes, restart Postfix with:

sudo systemctl restart postfix

Always check the status to ensure it’s running smoothly:

sudo systemctl status postfix

Testing Your Configuration

Once everything is configured, you can verify that your SMTP server is working correctly by sending a test email from the command line. Use the mail command:

echo "Test email body" | mail -s "Test Subject" user@example.com

If the recipient receives the email, you’ve successfully configured your SMTP server!

Common Issues and Troubleshooting

If you encounter issues, here are a few common checkpoints:

• Check your firewall settings to ensure port 25 (or the port you configured) is open.
• Review your mail logs in /var/log/mail.log or /var/log/maillog for errors.
• Ensure DNS records (MX records) for your domain are correctly configured.

Conclusion

Configuring an SMTP server in Linux is crucial for applications that require email notifications. Following this guide, you should have a fully functional SMTP setup.

Glossary of Terms

• SMTP: Simple Mail Transfer Protocol, the standard for sending emails.
• MTA: Mail Transfer Agent, a software that transfers email messages from one computer to another.

Pro Tips

• Regularly update your email server software to patch vulnerabilities.
• Consider implementing SSL/TLS for secure email transmission.

Setting Up Email Sending on Linux

Update: 26 Sep 2025