mx.ktk-sol.co.jp has no MX records.
Question and response
Question
dig mx.ktk-sol.co.jp. MX
Answer
The response has no answer records.
Authority
mx.ktk-sol.co.jp. 3600 SOA ns01.idcfcloud.com. sol-maintenance.actmail.net. 80 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0