Apex domains cannot have CNAME records.
Question and response
Question
dig cursemail.net. NS
Answer
cursemail.net. 4 NS ns-640.awsdns-16.net.
cursemail.net. 4 NS ns-1797.awsdns-32.co.uk.
cursemail.net. 4 NS ns-389.awsdns-48.com.
cursemail.net. 4 NS ns-1321.awsdns-37.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0