Apex domains cannot have CNAME records.
Question and response
Question
dig dilmail.com. NS
Answer
dilmail.com. 5 NS dil.datainfosys.net.
dilmail.com. 5 NS ns1.dildns.com.
dilmail.com. 5 NS ns2.dildns.com.
dilmail.com. 5 NS dil1.datainfosys.net.
Authority
The response has no authority records.
Additional
dil.datainfosys.net. 4 A 202.157.83.3
dil1.datainfosys.net. 4 A 202.157.81.3
ns1.dildns.com. 4 AAAA 2402:8c00:2:0:0:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0