Below we use Google App as an example.
1) Firstly, log into cPanel
2) Go to MX Entry
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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.
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Summary
- Set up the DNS pointing to the correct MX.
- Let the system detect the correct configuration for your MX.