mx.mirohost.net has no CNAME records.
Question and response
Question
dig mx.mirohost.net. NS
Answer
The response has no answer records.
Authority
mirohost.net. 899 SOA nsa2.srv53.net. support.dnshosting.org. 1771684424 1800 600 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0