mdmarkmx.maildealer.jp has no MX records.
Question and response
Question
dig mdmarkmx.maildealer.jp. MX
Answer
The response has no answer records.
Authority
maildealer.jp. 600 SOA ns-1672.awsdns-17.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0