mx.rackanddata.com has no CNAME records.
Question and response
Question
dig mx.rackanddata.com. NS
Answer
The response has no answer records.
Authority
rackanddata.com. 4840 SOA authns1.rackanddata.com. domainadmin.rackanddata.com. 1375326455 10800 3600 604800 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0