mail1.o2service.de has no NS records.
NS records for this zone are defined at o2service.de.
NS records for this zone are defined at o2service.de.
Question and response
Question
dig mail1.o2service.de. NS
Answer
The response has no answer records.
Authority
o2service.de. 600 SOA ns1.o2online.de. domain-de.o2.com. 2026022505 21600 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0