mailc40.carrierzone.com has no NS records.
NS records for this zone are defined at carrierzone.com.
NS records for this zone are defined at carrierzone.com.
Question and response
Question
dig mailc40.carrierzone.com. NS
Answer
The response has no answer records.
Authority
carrierzone.com. 1200 SOA ns1.carrierzone.com. admin.carrierzone.com. 2017082767 86400 3600 3600000 345600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0