Apex domains cannot have CNAME records.
Question and response
Question
dig zohomail.com. NS
Answer
zohomail.com. 5 NS ns21.zns-53.net.
zohomail.com. 5 NS pdns90.ultradns.net.
zohomail.com. 5 NS ns1.vtitan.com.
zohomail.com. 5 NS dns1.p03.nsone.net.
zohomail.com. 5 NS ns41.zns-53.net.
zohomail.com. 5 NS dns2.p03.nsone.net.
zohomail.com. 5 NS ns1.zohocorp.com.
zohomail.com. 5 NS ns11.zns-53.com.
zohomail.com. 5 NS pdns90.ultradns.com.
zohomail.com. 5 NS ns31.zns-53.com.
zohomail.com. 5 NS dns3.p03.nsone.net.
Authority
The response has no authority records.
Additional
ns1.vtitan.com. 5 A 165.173.187.13
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0