mta.windwireless.net has no MX records.
Question and response
Question
dig mta.windwireless.net. MX
Answer
The response has no answer records.
Authority
windwireless.net. 1800 SOA lucy.ns.cloudflare.com. dns.cloudflare.com. 2397165242 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0