mx.aams5.jp has no CNAME records.
Question and response
Question
dig mx.aams5.jp. NS
Answer
The response has no answer records.
Authority
aams5.jp. 300 SOA www1.aams.jp. aams-support.bbsec.co.jp. 2025111901 300 60 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0