This feature located in the cPanel will help to identify problems with your mail that is related DNS records for one or more of your domains. The feature uses these DNS records to verify that other servers can trust it as a sender. Basically this will help reduce the number of emails sent from server that may end up in spam folders.
The way that it works is that it will check the DKIM and SPF records to make sure they are valid for the server. DKIM verifies the sender and the integrity of a message. In addition, it allows an email system to prove that spammers did not alter an incoming message while in transit. SPF verifies that the messages your domains send originated from our server. In addition, it provides a list of servers approved to send mail from your domains.
How to check Email Deliverability
Fist you will need to log into your cPanel account and scroll down to the "EMAIL" section and click on "Email Deliverability"
Below in the image is an example on how it would look once the page loads up. In this image it shows examples of how it will appear when the system has found a problem and it will indicate what the issue is. In most case you will just need to click on "Repair" and it will resolve the issue. In cases where the "Repair" option is not available it would mean that the domain dns is not being hosted with us.
The "Manage" option will take you to a page that will display the default DKIM, SPF and PTR record for the server. It will also display if a problem exist for any of these records. You able to copy these records if you need them for a 3rd party email service that connects to the mail server.