Apex domains cannot have CNAME records.
Question and response
Question
dig mysmtp5.com. NS
Answer
mysmtp5.com. 3 NS pdns11.domaincontrol.com.
mysmtp5.com. 3 NS pdns12.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0