backend.nic-direct.de has no MX records.
Question and response
Question
dig backend.nic-direct.de. MX
Answer
The response has no answer records.
Authority
nic-direct.de. 300 SOA ns1.dnsresolve.net. root.ns1.dnsresolve.net. 2023120802 40000 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0