nsauth3.troycable.net has no MX records.
Question and response
Question
dig nsauth3.troycable.net. MX
Answer
The response has no answer records.
Authority
troycable.net. 300 SOA nsauth1.troycable.net. hostmaster.troycable.net. 2025090901 300 7200 1500000 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0