mx.windstream.net has no CNAME records.
Question and response
Question
dig mx.windstream.net. NS
Answer
The response has no answer records.
Authority
windstream.net. 2215 SOA ns5-auth.windstream.net. hostmaster.windstream.net. 2020102757 28800 7200 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0