mailout.server4you.de has no NS records.
NS records for this zone are defined at server4you.de.
NS records for this zone are defined at server4you.de.
Question and response
Question
dig mailout.server4you.de. NS
Answer
The response has no answer records.
Authority
server4you.de. 1800 SOA matt.ns.cloudflare.com. dns.cloudflare.com. 2393993889 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0