mx.acens.net has no NS records.
NS records for this zone are defined at acens.net.
NS records for this zone are defined at acens.net.
Question and response
Question
dig mx.acens.net. NS
Answer
The response has no answer records.
Authority
acens.net. 7200 SOA ns1.acens.net. hostmaster.acens.net. 1771895252 14400 3600 604800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0