mo1801.iij.ad.jp has no MX records.
Question and response
Question
dig mo1801.iij.ad.jp. MX
Answer
The response has no answer records.
Authority
iij.ad.jp. 3600 SOA bh0.iij.ad.jp. postmaster.iij.ad.jp. 1771949404 3600 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0