Easy Setup: Postfix Mail Server on Debian 12 Bookworm

This tutorial aims to guide you through the process of installing Postfix Mail Server on Debian 12 Bookworm and verifying your mail server setup using Telnet. Postfix is a widely used, free, and open-source mail transfer agent (MTA) well-suited for Linux-based systems. Setting up your own mail server can offer greater control and privacy compared to relying solely on third-party providers. This guide will walk you through each step, from initial installation to testing.

You can follow the steps below to install and configure Postfix Mail Server on Debian 12 Bookworm.

Install and Configure Postfix Mail Server on Debian 12 Bookworm

Before starting the setup of Postfix Mail Server on Debian 12, ensure you have access to your server as a non-root user with sudo privileges. You can consult a guide on Initial Server Setup with Debian 12 Bookworm if needed. After the initial setup is complete, follow the steps outlined below to successfully install and configure Postfix.

Step 1 – Postfix Installation on Debian 12

First, update your system’s package list by running the following command:

sudo apt update

This command ensures that you have the latest information about available packages.

Next, determine if any other MTA is already installed on your server. You can use the following command to check for services listening on port 25 (the standard SMTP port):

sudo netstat -ltnp |grep :25

If no MTA is installed, the command should return no output. In my case, I don’t have anything installed on my server.

Now, proceed with the installation of the Postfix mail server using the following command:

sudo apt install postfix

During the installation process, you will be prompted to select a configuration type.

Choose "Internet Site" and press OK to install Postfix with the default settings appropriate for a single server handling mail for a specific domain.

Next, you will be asked to enter your FQDN (Fully Qualified Domain Name) as your mail domain name. This is the domain that Postfix will use to identify itself when sending and receiving emails.

Once the installation is complete, you should see output similar to the following:

**Output**
Postfix (main.cf) is now set up with a default configuration.
...

You can verify the Postfix installation on Debian 12 by running the following command again:

netstat -ltnp |grep :25

**Output**
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      1902/master
tcp6       0      0 :::25                   :::*                    LISTEN      1902/master

This output confirms that Postfix is listening on port 25, indicating a successful installation. Note that Postfix is often referred to as "master" in system processes.

You can also check the mail logs for errors or information about Postfix’s operation:

# sudo cat /var/log/mail.log
# sudo cat /var/log/mail.errors
# sudo cat /var/log/mail.info

These commands will display the contents of the respective log files, providing insights into Postfix’s activity.

Step 2 – Postfix Configuration on Debian 12

For more advanced configuration of your Postfix installation, use the following command:

sudo dpkg-reconfigure postfix

This command will re-run the configuration wizard, allowing you to modify various settings. You’ll be prompted to select the mail server config type again; select "Internet Site" once more.

Then, you need to enter your FQDN (Fully Qualified Domain Name) as your Mail domain name again.

After setting up the mail domain, you will be asked to set up the user account of the system administrator, where all the mail will be redirected to. You can use this format "user@domain-name.com" and replace the user and domain names with those you have.

Next, you need to enter all the domains for which you want to receive the emails, and you also need to include the top-level domain.

At this point, you will be asked to choose whether to allow forced synchronous updates or not. If you want faster processing, you should keep it as "NO." It will come with a bit of risk of losing some emails during crashes, but with higher speeds, so it depends on your preference.

Now you will be prompted to select the network blocks for relaying mail. You can keep the default values for the Postfix mail server configuration to keep the host forwarding the emails to the local host. You can change it manually later on or set up a third-party mail service for relaying purposes.

From here three prompts will be for the mailbox size limit, local address extension character, and internet protocol selection. You can keep the default values for now or set your own as per your preferences. After doing so, Postfix will currently be configured with your settings.

Reload Postfix on Debian Linux

After making any configuration changes, reload the Postfix service to apply them:

sudo systemctl reload postfix

This command ensures that Postfix uses the updated configuration. You have now configured the basic settings of Postfix on your domain.

Step 3 – Test Postfix with Telnet

Since we have set up only the localhost mail server, will test it by running the telnet command on port 25 and see if the mail server is connected correctly.

Note: You can change localhost with your domain set up with Postfix.

telnet localhost 25

**Output**
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 localhost ESMTP Postfix (Debian/GNU)

This output indicates a successful connection to the mail server.

Now we want to send a test mail from a different domain to check if the mail is received correctly.

Send a Test Mail with Postfix

While staying connected to the mail server via Telnet, you need to run the following commands to create and send the test email:

mail from <<user-name>@<sender-domain.com>>

Replace <user-name> and <sender-domain.com> with the appropriate values.

rcpt to <<user-name>>

Replace this <user-name> with the root username account of your mail server. Now type "data" to enter email data and press ENTER.

data

Now enter the email data as follows:

From: <user-name@sender-domain.com>
To: <user-name@receiver-domain.com>
Subject: Enter your email subject here

Enter the body of the email here and then press ENTER.

To end the Telnet connection, type "." and press ENTER. Then type "quit" and press ENTER again.

.

quit

You can now check the inbox and see if you successfully received the test email sent from the other domain. You can execute the "mail" command to do so:

mail

For more information, you can visit Postfix Documentation.

Conclusion

At this point, you have learned to Install and Configure Postfix Mail Server on Debian 12 Bookworm Test your installation with Telnet and send a test mail with Postfix.

Hope you enjoy it. You may also like these articles:

Set up ClamAV Antivirus on Debian 12

Install and Configure WordPress on Debian 12

Alternative Solutions for Setting Up a Mail Server

While Postfix offers a robust and configurable solution, alternative approaches exist for setting up a mail server on Debian 12. Two such alternatives are discussed below.

1. Using Docker and a Pre-built Mail Server Image

Docker provides a containerization platform that allows you to run applications in isolated environments. This simplifies deployment and management, especially for complex services like mail servers. Several pre-built Docker images for mail servers are available, offering a quick and relatively easy way to get started. One popular option is mailu.

Explanation:

Using Docker eliminates the need to manually install and configure Postfix and its dependencies. The Docker image encapsulates everything needed, ensuring consistency across different environments. mailu is a full-featured mail server solution packed into a set of Docker images. It includes Postfix, Dovecot (an IMAP/POP3 server), and other essential components, such as an anti-spam filter and webmail interface.

Code Example:

First, install Docker on your Debian 12 system:

sudo apt update
sudo apt install docker.io
sudo systemctl start docker
sudo systemctl enable docker

Then, install Docker Compose:

sudo apt install docker-compose

Create a docker-compose.yml file with the following content (adjust the configuration as needed):

version: '3'
services:
  mailu:
    image: ghcr.io/mailu/mailu:latest
    container_name: mailu
    ports:
      - "25:25"   # SMTP
      - "80:80"   # HTTP (for webmail)
      - "110:110" # POP3
      - "143:143" # IMAP
      - "443:443" # HTTPS (for webmail)
      - "587:587" # Submission (MSA)
      - "993:993" # IMAPS
      - "995:995" # POP3S
    volumes:
      - ./data:/data
      - ./config:/config
    environment:
      - TZ=Europe/Berlin  # Replace with your timezone
      - MAILU_ADMIN_PASSWORD=your_admin_password
      - MAILU_DOMAIN=yourdomain.com
    restart: always

Replace your_admin_password and yourdomain.com with your desired values.

Finally, start the mail server:

docker-compose up -d

This command downloads the mailu image, creates the necessary containers, and starts the mail server in detached mode. You can then access the webmail interface through your server’s IP address or domain name.

2. Using a Simplified MTA like SSMTP

For scenarios where you only need to send emails from your server (e.g., for system notifications or automated scripts) and don’t require a full-fledged mail server, a simplified MTA like SSMTP can be a more lightweight and easier-to-configure solution.

Explanation:

SSMTP is a simple mail transfer agent designed primarily for sending emails to a mail hub (an external SMTP server). It doesn’t handle incoming mail or manage a local mailbox. It’s ideal for applications that need to send emails without the overhead of a full mail server. You’ll need an existing email account with an SMTP server (like Gmail, Outlook.com, or a dedicated email provider) to use SSMTP.

Code Example:

Install SSMTP on Debian 12:

sudo apt update
sudo apt install ssmtp

Configure SSMTP by editing the /etc/ssmtp/ssmtp.conf file:

sudo nano /etc/ssmtp/ssmtp.conf

Add the following lines (replace with your actual SMTP server details):

root=your_email@gmail.com
mailhub=smtp.gmail.com:587
rewriteDomain=yourdomain.com
hostname=yourdomain.com
UseTLS=YES
UseSTARTTLS=YES
AuthUser=your_email@gmail.com
AuthPass=your_email_password

• root: The email address that will be used as the sender for system emails.
• mailhub: The SMTP server and port to use.
• rewriteDomain: The domain to rewrite the sender address to.
• hostname: The hostname of your server.
• UseTLS and UseSTARTTLS: Enable secure connections.
• AuthUser and AuthPass: Your email address and password for authentication.

Important Security Note: Storing your email password directly in the configuration file is generally discouraged. Consider using application-specific passwords provided by your email provider, especially for services like Gmail.

Test SSMTP by sending a test email:

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

Replace recipient@example.com with the email address you want to send the test email to.

These alternative solutions offer different approaches to setting up mail functionality on Debian 12, depending on your specific needs and technical expertise. Choosing the right solution depends on whether you need a full-fledged mail server, a containerized solution, or a simple email sending agent. The Postfix Mail Server on Debian 12 Bookworm setup, however, remains a solid choice for a highly configurable and flexible mail server solution.