mail.ntf-server.net has no CNAME records.
Question and response
Question
dig mail.ntf-server.net. NS
Answer
The response has no answer records.
Authority
ntf-server.net. 5078 SOA dns1.nsdns.info. tech.key-systems.net. 2021020401 10800 3600 604800 28800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0