ns6-tk02.ocn.ad.jp has no MX records.
Question and response
Question
dig ns6-tk02.ocn.ad.jp. MX
Answer
The response has no answer records.
Authority
ocn.ad.jp. 600 SOA ns1.ocn.ad.jp. postmaster.ocn.ad.jp. 20395 10800 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0