ns2.mind.ad.jp has no MX records.
Question and response
Question
dig ns2.mind.ad.jp. MX
Answer
The response has no answer records.
Authority
mind.ad.jp. 900 SOA ns.mind.ad.jp. hostmaster.mind.ad.jp. 3000000029 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0