So, if a domain name is bought through Google for example and I want the web site to be hosted with Siteground and the email to remain with Google, I change the nameservers to the siteground server.
Then, I need to change the MX records via cpanel to the following:
Remote Mail Exchanger:
Priority 1 - ASPMX.L.GOOGLE.COM
Priority 5 - ALT1.ASPMX.L.GOOGLE.COM
Priority 5 - ALT2.ASPMX.L.GOOGLE.COM
Priority 10 - ALT3.ASPMX.L.GOOGLE.COM
Priority 10 - ALT4.ASPMX.L.GOOGLE.COM
If these are not added then the emails will not get through !