mx6.zoho.com has no CNAME records.
Question and response
Question
dig mx6.zoho.com. NS
Answer
The response has no answer records.
Authority
zoho.com. 268 SOA ns1.zohocorp.com. dnsadmin.vtitan.com. 2026022300 7200 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0