ns2.ambisys.jp has no MX records.
Question and response
Question
dig ns2.ambisys.jp. MX
Answer
The response has no answer records.
Authority
ambisys.jp. 1800 SOA ns0.ambisys.jp. hostmaster.ambisys.com. 2018080801 10800 1800 3600000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0