How to Configure Postfix only allow whitelisted Recipient Domain

Introduction

Learn how to configure Postfix to only allow emails to be sent to whitelisted recipient domains. This step-by-step guide includes user data for testing and minimizes the risk of sending emails to unwanted recipients.

In today's digital world, securing your email server is crucial. One effective method to enhance email security is by configuring Postfix to only allow whitelisted recipient domains. This guide will walk you through the process, providing clear examples and detailed steps to help you set up and test this configuration in your environment.

In this tutorial, How to Configure "Postfix only allow whitelisted Recipient Domain". We test environment with user data. To minimize the risk of sending to unwanted email recipients.

Configuring Postfix to Allow Only Whitelisted Recipient Domains

Step 1: Modify the main.cf File

To begin, you need to modify the Postfix main configuration file (main.cf) to specify the recipient restrictions. Open the main.cf file located in /etc/postfix/ and add the following line:

smtpd_recipient_restrictions = check_recipient_access hash:/etc/postfix/recipient_domains, reject

Note: The configuration line check_recipient_access hash:/etc/postfix/recipient_domains, reject ensures that only the domains listed in the recipient_domains file are allowed, and all others are rejected.

Step 2: Create the Whitelist File

Next, create the recipient_domains file to list the whitelisted domains:

sudo nano /etc/postfix/recipient_domains

Add the following lines to whitelist the specific domains:

mycompany.com    OK
mail.huuphan.com OK

Note: In this example, only mycompany.com and mail.huuphan.com are allowed to receive emails.

Step 3: Generate the Hash File

To enable Postfix to read the recipient_domains file, you need to convert it into a hash format:

sudo postmap /etc/postfix/recipient_domains

Step 4: Restart Postfix Service

Finally, restart the Postfix service to apply the changes:

sudo /etc/init.d/postfix restart

Testing the Configuration

After configuring Postfix, it’s important to test the setup to ensure it works correctly. Try sending an email to a domain not included in the whitelist. You should see an error message similar to this:

NOQUEUE: reject: RCPT from …: 554 5.7.1 <HuuPV@gmail.com>: Recipient address rejected: Access denied

Advanced Configuration

Adding More Restrictions

You can add additional restrictions to your Postfix configuration for enhanced security. Here’s how you can combine recipient and sender restrictions:

Edit the main.cf file to include sender access checks:

smtpd_recipient_restrictions = 
    permit_mynetworks,
    check_recipient_access hash:/etc/postfix/recipient_domains,
    check_sender_access hash:/etc/postfix/sender_access,
    reject_unauth_destination

Create the sender_access file to whitelist specific senders:

sudo nano /etc/postfix/sender_access

Add the whitelisted senders:

trusted@example.com    OK

Convert the sender_access file into a hash format:

sudo postmap /etc/postfix/sender_access

Restart Postfix to apply the changes:

sudo /etc/init.d/postfix restart

FAQs

What is Postfix?

Postfix is an open-source mail transfer agent (MTA) used to route and deliver electronic mail.

Why should I whitelist recipient domains?

Whitelisting recipient domains helps prevent unauthorized email delivery to untrusted domains, reducing the risk of spam and malicious emails.

How can I verify my Postfix configuration?

You can verify your Postfix configuration using the following command:

postfix check

What if my emails are still sent to non-whitelisted domains?

Ensure that your recipient_domains file is correctly formatted and converted using postmap. Also, check the main.cf file for the correct paths and parameters.

How can I log Postfix activity?

Edit the main.cf file to specify the log file location:

maillog_file = /var/log/mail.log

Then, monitor the logs using:

tail -f /var/log/mail.log

Conclusion

Configuring Postfix to only allow whitelisted recipient domains is a crucial step in securing your email server. By following the steps outlined in this guide, you can prevent unauthorized email delivery and ensure that your server is only communicating with trusted domains. If you have any questions or need further assistance, feel free to comment below.

This tutorial has provided a comprehensive guide to help you configure Postfix to only allow emails to be sent to whitelisted recipient domains, minimizing the risk of sending emails to unwanted recipients. Thank you for reading the huuphan.com page!