ns.ckp.jp has no MX records.
Question and response
Question
dig ns.ckp.jp. MX
Answer
The response has no answer records.
Authority
ckp.jp. 10800 SOA ckp.jp. root.ckp.jp. 2025122202 86400 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0