mail01.access4.com.au has no NS records.
NS records for this zone are defined at access4.com.au.
NS records for this zone are defined at access4.com.au.
Question and response
Question
dig mail01.access4.com.au. NS
Answer
The response has no answer records.
Authority
access4.com.au. 900 SOA ns-10.awsdns-01.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0