pluto.dnsrapid.net has no MX records.
Question and response
Question
dig pluto.dnsrapid.net. MX
Answer
The response has no answer records.
Authority
dnsrapid.net. 108000 SOA ns1.nsgrid.net. dns.nsgrid.net. 2015112655 108000 600 10800 108000
Additional
. 0 OPT ; payload 1224, xrcode 0, version 0, flags 0