smtp2.wappmail.com has no NS records.
NS records for this zone are defined at wappmail.com.
NS records for this zone are defined at wappmail.com.
Question and response
Question
dig smtp2.wappmail.com. NS
Answer
The response has no answer records.
Authority
wappmail.com. 300 SOA ns-cloud-b1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0