By using custom domain name(domain.com) to point to Google Hosted Apps email server in cPanel, you may refer to the step as below and change the MX record record from your cPanel.
Caution: Please do not modify the MX record if you are not sure on how to change it. You may submit a ticket in our Support Hub
Step 1: Login to your cPanel account.
Step 2: Click Mail.
Step 3: Click Modify Mail Exchanger (MX Entry). A list of your current MX records will appear.
Step 4: Click Change an MX Entry.
Step 5: In the Change MX for... filed, enter either of the list as below.
- ASPMX.L.GOOGLE.COM.
- ALT1.ASPMX.L.GOOGLE.COM.
- ALT2.ASPMX.L.GOOGLE.COM.
- ASPMX2.GOOGLEMAIL.COM.
- ASPMX3.GOOGLEMAIL.COM.
- ASPMX4.GOOGLEMAIL.COM.
- ASPMX5.GOOGLEMAIL.COM.
Note: Please be aware that there will be a dot(.) after the entry.
Step 6: Click Change.