ns2.dallas-idc.com has no MX records.
Question and response
Question
dig ns2.dallas-idc.com. MX
Answer
The response has no answer records.
Authority
dallas-idc.com. 2560 SOA ns1.limestonenetworks.com. noc.limestonenetworks.com. 1772571879 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0