mail.fiberstaden.net has no CNAME records.
Question and response
Question
dig mail.fiberstaden.net. NS
Answer
The response has no answer records.
Authority
fiberstaden.net. 900 SOA ns.fiberstaden.se. registry.fiberstaden.se. 2026030200 14800 7200 5184000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0