mx01.plutex.de has no CNAME records.
Question and response
Question
dig mx01.plutex.de. NS
Answer
The response has no answer records.
Authority
plutex.de. 300 SOA ns1.plutex.de. tech.plutex.de. 2026030202 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0