Postfix with Greylisting

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Cloud

Postfix with Greylisting

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.

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Lab Info

Level

Intermediate

Last updated

Aug 29, 2025

Duration

45m

Challenge

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.
Challenge

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.
Challenge

Configure the Postfix Configuration File to Use the Postgrey Service

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

Restart the Postfix email server.
Challenge

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

mailx
```
This should show you your email.

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