G Suite is our recommended solution for 3rd party email platforms.
Please note that Google changes their workflow and design often, so the steps below may not be 100% accurate at the time of reading. For the most up to date documentation from Google on this topic, please reference their documentation here: https://support.google.com/a/answer/172171?hl=en&ref_topic=2705493
To verify a G Suite Account please follow these instructions -
Go to https://gsuite.google.com/products/gmail/ and click on "Get Started":
Google also provides a free service to have them help with the setup: Set up G Suite for your organization.
Now it is time to add one of the ways provided by Google for the "Verification Step" -
2. TXT Record:
Login to the admin of a website and go to Developer Hub » cPanel Dashboard » "Zone Editor":
Inside the DNS Zone Editor click on "Manage":
Add the records for the site: