mx20.system-hoster.com has no CNAME records.
Question and response
Question
dig mx20.system-hoster.com. NS
Answer
The response has no answer records.
Authority
system-hoster.com. 4501 SOA dns.dns1.de. hostmaster.internetwire.de. 2025121701 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0