mfi31.securemx.jp has no MX records.
Question and response
Question
dig mfi31.securemx.jp. MX
Answer
The response has no answer records.
Authority
securemx.jp. 3600 SOA dns0.iij.ad.jp. postmaster.iij.ad.jp. 100651 3600 1800 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0