How to perform a test Callout / Callback  Verification

Introduction

You may use the following procedure for testing Callback / Callout Verifications

The following resource provides more context about this:

What is the difference between "Sender Verification" and "Sender Verification Callouts" in the Exim Configuration Manager?

Procedure

Login to your cPanel server via SSH as the root user

Install telnet with the following command:

yum install telnet -y

Find the MX server of the domain for the address that you are testing with the following command:

dig +short domain.tld MX

Use telnet to connect to the MX server on port 25:

telnet mx1.domain.tld 25

Issue the following commands:

HELO any.hostname.tld
MAIL FROM:<>
RCPT TO:<sender@domain.tld>

If you get the following in response it means that the callback verification succeeded and the email address does exist on the server:

250 Accepted