voip.cableone.net has no MX records.
Question and response
Question
dig voip.cableone.net. MX
Answer
The response has no answer records.
Authority
voip.cableone.net. 900 SOA ns1.cableone.net. dnsadmin.cableone.net. 381 10800 3600 2592000 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0