Apex domains cannot have CNAME records.
Question and response
Question
dig sanmargroup.com. NS
Answer
sanmargroup.com. 5 NS ns49.domaincontrol.com.
sanmargroup.com. 5 NS ns50.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0