Setting Up Postfix to Send Email Through Gmail

Introduction

Setting up email notifications is a critical task in homelab management. Services like Proxmox and OPNsense benefit greatly from reliable email alerts for updates, backups, or critical events. Configuring Postfix to send emails through Gmail provides a straightforward and secure solution. This guide will walk you through the steps to set up Postfix on a Linux system to relay emails using Gmail’s SMTP server.

Prerequisites

Before you begin, ensure the following:

1. A Linux system with Postfix installed.
2. A Gmail account with an app password enabled (explained below).
3. Basic terminal access and permissions to edit configuration files.

Why Use an App Password?

Google enforces stricter security measures for less secure apps. You’ll need to generate an app password specifically for Postfix:

1. Log in to your Google account.
2. Go to Manage Your Google Account > Security.
3. Under Signing in to Google, enable 2-Step Verification if not already enabled.
4. Once 2-Step Verification is active, return to the Security page and find App Passwords.
5. Create a new app password for “Mail” or “Other” and note it down for later.

Step 1: Install Postfix

If Postfix is not already installed, install it using your distribution’s package manager. For example:

sudo apt update
sudo apt install postfix -y

During installation, choose “Internet Site” when prompted, and set the system mail name (e.g., yourdomain.com).

Step 2: Configure Postfix for Gmail SMTP

Edit the Postfix configuration file to use Gmail as the relay host. Open /etc/postfix/main.cf in your preferred text editor and fill out the following:

relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

Create the Password File

Create a password file at /etc/postfix/sasl_passwd to store your Gmail credentials:

[smtp.gmail.com]:587 your-email@gmail.com:your-app-password

Replace your-email@gmail.com with your Gmail address and your-app-password with the app password generated earlier.

Secure and Hash the Password File

Secure the file permissions, and hash the file using postmap:

sudo chmod 600 /etc/postfix/sasl_passwd
sudo postmap /etc/postfix/sasl_passwd

Step 3: Restart Postfix

Restart the postfix service on your linux machine.

sudo systemctl restart postfix

Step 4: Test the Setup

Test your configuration by sending a test email. Use the mail command or another mail client installed on your system:

echo "This is a test email." | mail -s "Test Email" recipient@example.com

Chcek the logs if the email fails to send:

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

Step 5: Troubleshooting Common Issues

• Authentication errors: Double-check the app password and ensure sasl_passwd is correctly hashed.
• Firewall blocking SMTP: Ensure ports 587 (for Gmail SMTP) are open.
• Incorrect CA certificates: Ensure /etc/ssl/certs/ca-certificates.crt exists or specify a valid CA file.

Conclusion

Configuring Postfix to send emails through Gmail enables reliable email notifications for your homelab services.