How we can disable mails from a particular domain on Cpanel?
Step 1 :- Login to WHM and go to Main >> DNS Functions >> Edit MX Entry for the example.com
Step 2 :- Edit the Domain example.com.
Step 3 :- choose "Remote Mail Exchanger" this will Configure server to not accept mail locally and send mail to the lowest MX record.
Step 4 :- Than Click on Save button.
Note :- If example.com are Not pointed to your dns and just use IP forwarding to run on your server you can remove the dns entry for example.com by delete the dns zone for example.com as it not used.