When a domain is hosted with us but there is a need to use an external mail service such as Gmail or Outlook, certain changes will need to be made.
Firstly, within cPanel, under the Mail Routing option, Remote should be selected and saved. This tells cPanel that it will no longer deal with email for the domain and mail sent from the server (such as from the website) for this domain will not be handled locally. This is a crucial step to ensure that cPanel does not make any further changes to the zone file or MX records on future updates.
Moving on to the DNS zone, which can be edited via the Zone Editor tool, you should remove any and all previously listed MX records and then add your own provided by the third party. Once set, these can take up to 72 hours to propagate, so having a planned migration path should be made prior to the changes.
It is important to always set the routing option accordingly and Local or Remote should only be used. Backup should only be used if you know what you are doing and the technical requirements to use this.
Automatic should not be used because it does not set either option hard on the domain and routing is essentially fluid based on real time checks.
The default for all created domains in cPanel is Local.