mx.nexmart.net has no CNAME records.
Question and response
Question
dig mx.nexmart.net. NS
Answer
The response has no answer records.
Authority
nexmart.net. 3028 SOA ns.inwx.de. hostmaster.inwx.de. 2025032400 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0