cdnetworks.net.2.arsmtp.com has no NS records.
NS records for this zone are defined at arsmtp.com.
NS records for this zone are defined at arsmtp.com.
Question and response
Question
dig cdnetworks.net.2.arsmtp.com. NS
Answer
The response has no answer records.
Authority
arsmtp.com. 600 SOA mdns1.appriver.com. support.appriver.com. 11145434 900 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0