mail.dnsrapid.net has no CNAME records.
Question and response
Question
dig mail.dnsrapid.net. NS
Answer
The response has no answer records.
Authority
dnsrapid.net. 9577 SOA ns1.nsgrid.net. dns.nsgrid.net. 2015112655 108000 600 10800 108000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0