smtppool.wkb.be has no NS records.
NS records for this zone are defined at wkb.be.
NS records for this zone are defined at wkb.be.
Question and response
Question
dig smtppool.wkb.be. NS
Answer
The response has no answer records.
Authority
wkb.be. 300 SOA ns1-34.azure-dns.com. azuredns-hostmaster.microsoft.com. 1 3600 300 2419200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0