oldmail.mirae.com has no CNAME records.
Question and response
Question
dig oldmail.mirae.com. NS
Answer
The response has no answer records.
Authority
mirae.com. 600 SOA mirae.com. root.mirae.com. 2017061401 3600 1200 864000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0