Configure Postfix MTA as Send-Only on Debian 10 / 11

In this guide we’ll look at how you can configure Postfix MTA as a send-only SMTP server on Debian 10/11, meaning it doesn’t receive and process emails. Its job is only to act as Local mail transfer agent. Postfix is a popular open source Mail Transfer Agent (MTA) used in Linux and Unix environments.

A send only mail server is useful especially when used in scripting, e.g having a cron job that sends an email about the status of its execution, or an application that sends an email to you when certain events happen.

Configure Postfix as a Send-Only SMTP Server on Debian 10/11

Installing and configuring Postfix as a Send-Only SMTP Server on Debian 11|10 is an easy process. Start by updating your system

sudo apt update

Also set a hostname for the server so that emails will show a from address with valid domain section.

sudo hostnamectl set-hostname smtp.example.com --static

Install mailutils package other mail utilities.

sudo apt install mailutils

Finally install postfix:

sudo apt install postfix

As the package installs, you’ll be asked to select an option on screen for your mail server. For “General type of email configuration” window, select Internet site and click OK button.

The next page will ask you to set your Mail server name, this can be domain or server hostname with an A record.

Select OK to save the settings and finish the installation.

Configure Postfix MTA Server

Edit Postfix configuration file /etc/postfix/main.cf to ensure it is configured as send only ( Only relaying emails from the local server).

Set Postfix to listen on the 127.0.0.1 loopback interface. The default setting is to listen on all interfaces.

inet_interfaces = loopback-only

Also, set myhostname to your Server FQDN

myhostname=smtp.example.com

Restart Postfix service for it to pick the new changes,

sudo systemctl restart postfix

You have successfully installed and configured Postfix as a Send only MTA server on Debian 10/11. To test email delivery, use the mail command like below

echo "Postfix Send-Only Server" | mail -s "Postfix Testing" userx@example.com

And that’s it, if you have any questions please leave a comment. 🙂