Apex domains cannot have CNAME records.
Question and response
Question
dig xmailse.com. NS
Answer
xmailse.com. 5 NS ns-12.awsdns-01.com.
xmailse.com. 5 NS ns-818.awsdns-38.net.
xmailse.com. 5 NS ns-1049.awsdns-03.org.
xmailse.com. 5 NS ns-1834.awsdns-37.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0