pool.mitene.or.jp has no MX records.
Question and response
Question
dig pool.mitene.or.jp. MX
Answer
The response has no answer records.
Authority
pool.mitene.or.jp. 600 SOA nsx1.mitene.ad.jp. postmaster.po.mitene.or.jp. 100064 7200 1800 1209600 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0