mail.ymir.jp has no CNAME records.
Question and response
Question
dig mail.ymir.jp. NS
Answer
The response has no answer records.
Authority
ymir.jp. 720 SOA dns1.ymir.jp. server.ymir.co.jp. 2026030302 28800 1440026 604800 720
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0