mx.acens.com has no NS records.
NS records for this zone are defined at acens.com.
NS records for this zone are defined at acens.com.
Question and response
Question
dig mx.acens.com. NS
Answer
The response has no answer records.
Authority
acens.com. 2128 SOA ns1.acens.net. hostmaster.ns1.acens.net. 1771826047 14400 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0