mail.zoho.com has no CNAME records.
Question and response
Question
dig mail.zoho.com. NS
Answer
The response has no answer records.
Authority
zoho.com. 286 SOA ns1.zohocorp.com. dnsadmin.vtitan.com. 2026030400 7200 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0