mail-6.sosafe.de has no NS records.
NS records for this zone are defined at sosafe.de.
NS records for this zone are defined at sosafe.de.
Question and response
Question
dig mail-6.sosafe.de. NS
Answer
The response has no answer records.
Authority
sosafe.de. 900 SOA ns-612.awsdns-12.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0