smtp.MYNET.JP has no MX records.
Question and response
Question
dig smtp.MYNET.JP. MX
Answer
The response has no answer records.
Authority
MYNET.JP. 3600 SOA NS21.FreeBit.NET. root.FreeBit.NET. 2019052901 3600 900 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0