mx1.neustar.com has no CNAME records.
Question and response
Question
dig mx1.neustar.com. NS
Answer
The response has no answer records.
Authority
neustar.com. 9721 SOA udns1.ultradns.net. networkers.neustar.biz. 1311363932 86400 86400 86400 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0