mx-dor.bell.ca has no CNAME records.
Question and response
Question
dig mx-dor.bell.ca. NS
Answer
The response has no answer records.
Authority
bell.ca. 900 SOA mtl02vnszs08.srvr.bell.ca. dns-admin.bellglobal.com. 99042419 7200 3600 2419200 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0