mail-au1.hostid.net has no NS records.
NS records for this zone are defined at hostid.net.
NS records for this zone are defined at hostid.net.
Question and response
Question
dig mail-au1.hostid.net. NS
Answer
The response has no answer records.
Authority
hostid.net. 900 SOA ns-1719.awsdns-22.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0