mx6.basmail.jp has no CNAME records.
Question and response
Question
dig mx6.basmail.jp. NS
Answer
The response has no answer records.
Authority
basmail.jp. 600 SOA dns0.tokai.or.jp. postmaster.tokai.or.jp. 20250901 3600 300 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0