frontend.nicdirect.de has no MX records.
Question and response
Question
dig frontend.nicdirect.de. MX
Answer
The response has no answer records.
Authority
nicdirect.de. 900 SOA ns1.dnsresolve.net. root.ns1.dnsresolve.net. 2023082301 40000 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0