mailf.fusixnetworks.net has no CNAME records.
Question and response
Question
dig mailf.fusixnetworks.net. NS
Answer
The response has no answer records.
Authority
fusixnetworks.net. 10800 SOA ns0.fusixnetworks.net. hostmaster.fusix.nl. 2026030504 10800 1800 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0