mx.activegate-ss.jp has no MX records.
Question and response
Question
dig mx.activegate-ss.jp. MX
Answer
The response has no answer records.
Authority
activegate-ss.jp. 900 SOA ns-2033.awsdns-62.co.uk. awsdns-hostmaster.amazon.com. 2015080401 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0