dmail.kagoya.net has no CNAME records.
Question and response
Question
dig dmail.kagoya.net. NS
Answer
The response has no answer records.
Authority
kagoya.net. 600 SOA ns.kagoya.net. root.kagoya.net. 2026030600 3900 300 360000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0