mx.bell.net has no NS records.
NS records for this zone are defined at bell.net.
NS records for this zone are defined at bell.net.
Question and response
Question
dig mx.bell.net. NS
Answer
The response has no answer records.
Authority
bell.net. 900 SOA tor63vnszp08.srvr.bell.ca. trademarks.bell.ca. 6530 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0