mx1-old.mirohost.net has no CNAME records.
Question and response
Question
dig mx1-old.mirohost.net. NS
Answer
The response has no answer records.
Authority
mirohost.net. 900 SOA nsa2.srv53.net. support.dnshosting.org. 1772027118 1800 600 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0