inmail.zycus.com has no CNAME records.
Question and response
Question
dig inmail.zycus.com. NS
Answer
The response has no answer records.
Authority
zycus.com. 600 SOA a1-16.akam.net. hostmaster.akamai.com. 2019085777 3600 900 1728000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0