IIJNET.IIJ.NET has no MX records.
Question and response
Question
dig IIJNET.IIJ.NET. MX
Answer
The response has no answer records.
Authority
iij.net. 18000 SOA dns0.iij.ad.jp. postmaster.iij.ad.jp. 103180 3600 1800 3600020 18000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0