mx4.windstreambiz.net has no CNAME records.
Question and response
Question
dig mx4.windstreambiz.net. NS
Answer
The response has no answer records.
Authority
windstreambiz.net. 5292 SOA cns01.windstream.net. hostmaster.windstream.net. 2019050645 28800 14400 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0