mx.plugmeon.com has no NS records.
NS records for this zone are defined at plugmeon.com.
NS records for this zone are defined at plugmeon.com.
Question and response
Question
dig mx.plugmeon.com. NS
Answer
The response has no answer records.
Authority
plugmeon.com. 3600 SOA dns.plugmeon.com. hostmaster.plugmeon.com. 1527380378 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0