mail.greenradar.com has no CNAME records.
Question and response
Question
dig mail.greenradar.com. NS
Answer
The response has no answer records.
Authority
greenradar.com. 600 SOA pdns07.domaincontrol.com. dns.jomax.net. 2026030200 28800 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0