mx.grantbranding.com has no CNAME records.
Question and response
Question
dig mx.grantbranding.com. NS
Answer
The response has no answer records.
Authority
grantbranding.com. 3279 SOA dns.grantbranding.com. hostmaster.grantbranding.com. 1383511888 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0