mail.kirub2.de has no NS records.
NS records for this zone are defined at kirub2.de.
NS records for this zone are defined at kirub2.de.
Question and response
Question
dig mail.kirub2.de. NS
Answer
The response has no answer records.
Authority
kirub2.de. 3600 SOA hydrogen.ns.hetzner.com. dns.hetzner.com. 2025062401 86400 10800 3600000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0