mx.mangohost.net has no NS records.
NS records for this zone are defined at mangohost.net.
NS records for this zone are defined at mangohost.net.
Question and response
Question
dig mx.mangohost.net. NS
Answer
The response has no answer records.
Authority
mangohost.net. 7200 SOA ns1.topdns.me. hostmaster.mangohost.net. 1766769301 10800 3600 432000 38400
Additional
The response has no additional records.