mx04.fischl.online has no CNAME records.
Question and response
Question
dig mx04.fischl.online. NS
Answer
The response has no answer records.
Authority
fischl.online. 300 SOA ns03.fischl.online. root.fischl-online.de. 1772505743 3600 7200 2419200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0