ns2.comcastbusiness.net has no MX records.
Question and response
Question
dig ns2.comcastbusiness.net. MX
Answer
The response has no answer records.
Authority
comcastbusiness.net. 900 SOA ns.comcastbusiness.net. domregtech.comcastonline.com. 2008113807 7200 300 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0