mx.cogeco.net has no NS records.
NS records for this zone are defined at cogeco.net.
NS records for this zone are defined at cogeco.net.
Question and response
Question
dig mx.cogeco.net. NS
Answer
The response has no answer records.
Authority
cogeco.net. 300 SOA ns1.cgocable.net. dnsadmin.cgocable.net. 2008205298 1800 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0