mx01.dcsix.net has no NS records.
NS records for this zone are defined at dcsix.net.
NS records for this zone are defined at dcsix.net.
Question and response
Question
dig mx01.dcsix.net. NS
Answer
The response has no answer records.
Authority
dcsix.net. 300 SOA ns1.dcsix.net. hostmaster.dcsix.net. 2015120638 14400 3600 604800 300
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0