smtp.idc.jp has no MX records.
Question and response
Question
dig smtp.sharedmail.jp. MX
Answer
The response has no answer records.
Authority
smtp.sharedmail.jp. 3600 SOA ns01.idcfcloud.com. domain.seeds.ne.jp. 226 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0