ns.kunden.de has no MX records.
Question and response
Question
dig ns.kunden.de. MX
Answer
The response has no answer records.
Authority
kunden.de. 600 SOA theopolis.uni-X.net. hostmaster.avency.de. 2025090102 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0