mail.instra.com has no CNAME records.
Question and response
Question
dig mail.instra.com. NS
Answer
The response has no answer records.
Authority
instra.com. 60 SOA ns1.instra.net.au. admin.instra.com. 2026020301 300 600 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0