mail.ns3.dnsbox.net has no CNAME records.
Question and response
Question
dig mail.ns3.dnsbox.net. NS
Answer
The response has no answer records.
Authority
ns3.dnsbox.net. 3736 SOA ns.dnsbox.net. hostmaster.dnsbox.net. 2014061011 10000 3600 604800 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0