Apex domains cannot have CNAME records.
Question and response
Question
dig mailtastic.com. NS
Answer
mailtastic.com. 5 NS ns77.domaincontrol.com.
mailtastic.com. 5 NS ns78.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0