mail.dsi.net has no CNAME records.
Question and response
Question
dig mail.dsi.net. NS
Answer
The response has no answer records.
Authority
dsi.net. 1404 SOA ns.dsinet.eu. hostmaster.dsi.net. 2026022200 28800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0