mta.tanomail.com has no CNAME records.
Question and response
Question
dig mta.tanomail.com. NS
Answer
The response has no answer records.
Authority
tanomail.com. 386 SOA ns2.otsuka-shokai.co.jp. root.otsuka-shokai.co.jp. 2025121501 10800 3600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0