mx1.jpberlin.de has no NS records.
NS records for this zone are defined at jpberlin.de.
NS records for this zone are defined at jpberlin.de.
Question and response
Question
dig mx1.jpberlin.de. NS
Answer
The response has no answer records.
Authority
jpberlin.de. 1800 SOA ns.jpberlin.de. root.jpberlin.de. 2014830896 14400 1800 604800 86400
Additional
. 0 OPT ; payload 1480, xrcode 0, version 0, flags 0