mx.dnsassurance.com has no CNAME records.
Question and response
Question
dig mx.dnsassurance.com. NS
Answer
The response has no answer records.
Authority
dnsassurance.com. 8090 SOA av4.nstld.com. nstld.verisign-grs.com. 1772842709 1800 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0