How do I enable Pop-before-SMTP on my cPanel server?

Introduction

Administrators who want their server to utilize POP before SMTP can follow the steps below to enable this configuration option. 

Please note, that it is not recommended to enable this feature, and it can lead to mail abuse. When a user authenticates, the IP of that user is whitelisted for future email for the next 30 minutes, and this allows someone on the same network to send without restriction.

Procedure

To adjust this, please follow the steps below.

1. Access the WHM interface as the root user.
2. Navigate to "Home / Server Configuration / Tweak Settings" 
3. Enable the following setting:

   Allow users to relay mail if they use an IP address through which someone has validated an IMAP or POP3 login within the last hour (Pop-before-SMTP)

4. Scroll to the bottom and save the setting. 

Additional Resources

Tweak Settings