mx.bell.net has no CNAME records.
Question and response
Question
dig mx.bell.net. NS
Answer
The response has no answer records.
Authority
bell.net. 883 SOA tor63vnszp07.srvr.bell.ca. trademarks.bell.ca. 6530 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0