ri.cox.net has no MX records.
Question and response
Question
dig ri.cox.net. MX
Answer
The response has no answer records.
Authority
ri.cox.net. 86400 SOA dukensumpov1z.services.cox.net. hostmaster.cox.net. 781212351 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0