mx4.vianet.ca has no CNAME records.
Question and response
Question
dig mx4.vianet.ca. NS
Answer
The response has no answer records.
Authority
vianet.ca. 635 SOA gwn.vianet.ca. hostmaster.vianet.ca. 1772046733 600 900 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0