ns.xb-test760.awk.jp has no MX records.
Question and response
Question
dig ns.xb-test760.awk.jp. MX
Answer
The response has no answer records.
Authority
xb-test760.awk.jp. 3600 SOA ns.xb-test760.awk.jp. akio\.shimonishi.rakus.co.jp. 2020100505 14400 60 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0