dc.cox.net has no MX records.
Question and response
Question
dig dc.cox.net. MX
Answer
The response has no answer records.
Authority
dc.cox.net. 86400 SOA dukensumpov1z.services.cox.net. hostmaster.cox.net. 781212229 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0