mx3.vist.is has no NS records.
NS records for this zone are defined at vist.is.
NS records for this zone are defined at vist.is.
Question and response
Question
dig mx3.vist.is. NS
Answer
The response has no answer records.
Authority
vist.is. 900 SOA ns-2013.awsdns-59.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0