Below we use Google App as an example.
1) Firstly, log into cPanel
2) Go to MX Entry
3) Now make sure it only contain entries pointing to google or other remote MX.
4) Select 'Automatically Detect Configuration' and it should say 'Remote' after you save it.
- Set up the DNS pointing to the correct MX.
- Let the system detect the correct configuration for your MX.