Apex domains cannot have CNAME records.
Question and response
Question
dig zeptomail.in. NS
Answer
zeptomail.in. 4 NS NS21.ZNS-53.NET.
zeptomail.in. 4 NS NS31.ZNS-53.COM.
zeptomail.in. 4 NS PDNS90.ULTRADNS.COM.
zeptomail.in. 4 NS PDNS90.ULTRADNS.BIZ.
zeptomail.in. 4 NS NS1.ZOHOCORP.COM.
zeptomail.in. 4 NS NS41.ZNS-53.NET.
zeptomail.in. 4 NS NS11.ZNS-53.COM.
zeptomail.in. 4 NS PDNS90.ULTRADNS.NET.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0