mail.telstraglobal.net has no CNAME records.
Question and response
Question
dig mail.telstraglobal.net. NS
Answer
The response has no answer records.
Authority
telstraglobal.net. 895 SOA ns03.telstraglobal.net. ipnoc.telstraglobal.net. 2026030300 3600 3600 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0