smtp-fo.knology.synacor.com has no MX records.
Question and response
Question
dig smtp-fo.knology.synacor.com. MX
Answer
The response has no answer records.
Authority
synacor.com. 3600 SOA dns1.p05.nsone.net. hostmaster.nsone.net. 1653325586 3600 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0