ns06.pwd.ne.jp has no MX records.
Question and response
Question
dig ns06.pwd.ne.jp. MX
Answer
The response has no answer records.
Authority
pwd.ne.jp. 300 SOA tegami1.int-gw.kddi.ne.jp. admin.int-gw.kddi.ne.jp. 2014120101 600 180 3600000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0