mx01.exfort.net has no CNAME records.
Question and response
Question
dig mx01.exfort.net. NS
Answer
The response has no answer records.
Authority
exfort.net. 2446 SOA ns6.intervia.ad.jp. ns-admin.intervia.ad.jp. 2025060500 3600 900 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0