mx1820R-stg.dx.2iij.net has no CNAME records.
Question and response
Question
dig mx1820R-stg.dx.2iij.net. NS
Answer
The response has no answer records.
Authority
dx.2iij.net. 10800 SOA dns0.iij.ad.jp. postmaster.iij.ad.jp. 100165 3600 1800 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0