mx04.agn-e.net has no CNAME records.
Question and response
Question
dig mx04.agn-e.net. NS
Answer
The response has no answer records.
Authority
agn-e.net. 300 SOA ns1.cyso.nl. hostmaster.agn-e.net. 1549957130 1800 1800 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0