mx.ispn.net has no CNAME records.
Question and response
Question
dig mx.ispn.net. NS
Answer
The response has no answer records.
Authority
ispn.net. 312 SOA ns1.ispn.net. administrator.ispn.net. 2026022000 1800 800 864000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0