mx2.isvoip.net has no CNAME records.
Question and response
Question
dig mx2.isvoip.net. NS
Answer
The response has no answer records.
Authority
isvoip.net. 301 SOA ns1.is.co.za. support.is.co.za. 2022030702 28800 7200 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0