mx1.denic.de has no NS records.
NS records for this zone are defined at denic.de.
NS records for this zone are defined at denic.de.
Question and response
Question
dig mx1.denic.de. NS
Answer
The response has no answer records.
Authority
denic.de. 1800 SOA ns1.denic.de. dns-operations.denic.de. 1771838600 10800 1800 3600000 1800
Additional
. 0 OPT ; payload 1452, xrcode 0, version 0, flags 0