rad2.xsp.ne.jp has no MX records.
Question and response
Question
dig rad2.xsp.ne.jp. MX
Answer
The response has no answer records.
Authority
xsp.ne.jp. 300 SOA milkroad.magma.ad.jp. tech.magma.ad.jp. 2020111101 10800 3600 604800 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0