Postfix with Greylisting

45 minutes
  • 4 Learning Objectives

About this Hands-on Lab

In this lab, you will be provided with a Linux CentOS server that has Postfix and greylisting installed but not configured. Your task is to configure the software so that incoming emails are sent through the greylisting process.

The purpose of this lab is to have you configure Postfix to use the greylisting policy.

Once configured, you will verify that Postfix is directing incoming email through the greylisting process.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Log In to the Provided Server

Log in to the server as cloud_user with the provided password. When the SERVER-READY file is shown in the /home/cloud_user folder, you can then follow along with the tasks.

Install the Postgrey Greylisting Software

Using the dnf or yum system commands, install the postgrey package. Start the software and set it to auto-start on system reboot.

Configure the Postfix Configuration File to Use the Postgrey Service

Edit the /etc/postfix/ file and add the Postgrey policy service so incoming emails get greylisted on arrival.

Restart the Postfix email server.

Test That Postgrey Is Intercepting Emails

Test that the Postfix service is using Postgrey to intercept emails.

When testing, you should see a Recipient address rejected message.

When you retry after 60 seconds, the email should now be accepted.

An example of using the telnet program to connect to a local email system is as follows:

telnet localhost 25

ehlo localhost
mail from: cloud_user
rcpt to: testuser

At this time, you should see a message saying you have been greylisted for 60 seconds.

Wait 60 seconds and try the command again:

rcpt to: testuser

This should allow you to continue with the task of sending email data.

Now you can test by using the su command to sudo to the testuser and checking email.

su - testuser


This should show you your email.

Additional Resources

You have heard that there is something called greylisting that can be used with Postfix.

You also heard that it introduces a delay in receiving email but can stop spammers from sending you emails.

You have a server that has Postfix installed and configured for testing, but it hasnt been configured to use greylisting, even though greylisting has been installed via the Postgrey software package.

You will use the preinstalled server and update the Posfix configuration to use the Postgrey software configuration file with greylisting.

You will then test that it is working.

What are Hands-on Labs

Hands-on Labs are real environments created by industry experts to help you learn. These environments help you gain knowledge and experience, practice without compromising your system, test without risk, destroy without fear, and let you learn from your mistakes. Hands-on Labs: practice your skills before delivering in the real world.

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