smtp1-ext.dfw1.corp.rackspace.com has no AAAA records.
Question and response
Question
dig smtp1-ext.dfw1.corp.rackspace.com. AAAA
Answer
The response has no answer records.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0