mx.nexmart.com has no CNAME records.
Question and response
Question
dig mx.nexmart.com. NS
Answer
The response has no answer records.
Authority
nexmart.com. 3592 SOA ns.inwx.de. hostmaster.inwx.de. 2026030412 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0