Apex domains cannot have CNAME records.
Question and response
Question
dig 1-grid-mx02.com. NS
Answer
1-grid-mx02.com. 5 NS venus.ns.1-grid.co.uk.
1-grid-mx02.com. 5 NS venus.ns.1-grid.com.
1-grid-mx02.com. 5 NS venus.ns.1-grid.co.za.
1-grid-mx02.com. 5 NS venus.ns.1-grid.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0