webmail.optonline.net has no NS records.
NS records for this zone are defined at optonline.net.
NS records for this zone are defined at optonline.net.
Question and response
Question
dig webmail.optonline.net. NS
Answer
The response has no answer records.
Authority
optonline.net. 900 SOA authns1.cv.net. hostmaster.cv.net. 86273 7200 600 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0