Allows you to search a variety of questions and answers
One way to fix this is as follows:
1. Login to your WHM as root and click on Exim Configuration Editor on your left.
2. Uncheck the box that says: Use callouts to verify the existence of email senders and Save.
3. Go back to the Editor and click the Advanced Editor button.
4. Do a search for sender/callout.
5. When you find it, delete 'callout' and leave only 'sender'. Save.
Without doubt the most professional and friendly support team i have ever experienced. These guys are really way above any other company i have worked with in the past.