Apex domains cannot have CNAME records.
Question and response
Question
dig xetmail.com. NS
Answer
xetmail.com. 3 NS ns1.atw.hu.
xetmail.com. 3 NS ns5.atw.hu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0