smtp.rzone.de has no NS records.
NS records for this zone are defined at rzone.de.
NS records for this zone are defined at rzone.de.
Question and response
Question
dig smtp.rzone.de. NS
Answer
The response has no answer records.
Authority
rzone.de. 3600 SOA karlsruhe.nic.xlink.net. de-domain.xlink.net. 2026022700 3600 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0