mx23.exchange.telus.com has no CNAME records.
Question and response
Question
dig mx23.exchange.telus.com. NS
Answer
The response has no answer records.
Authority
exchange.telus.com. 1477 SOA dns41.telus.com. dnsadmin2.telus.com. 2018042421 900 7200 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0