Apex domains cannot have CNAME records.
Question and response
Question
dig mta.hdems.com. NS
Answer
mta.hdems.com. 5 NS ns-1075.awsdns-06.org.
mta.hdems.com. 5 NS ns-177.awsdns-22.com.
mta.hdems.com. 5 NS ns-632.awsdns-15.net.
mta.hdems.com. 5 NS ns-1807.awsdns-33.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0