mdp.comcast.net has no MX records.
Question and response
Question
dig mdp.comcast.net. MX
Answer
The response has no answer records.
Authority
mdp.comcast.net. 900 SOA dns101.comcast.net. dnsadmin.comcast.net. 148 7200 3600 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0