mx.mailserv.nu has no CNAME records.
Question and response
Question
dig mx.mailserv.nu. NS
Answer
The response has no answer records.
Authority
mailserv.nu. 3383 SOA ns1.dnsserv.se. registry.dnsserv.se. 2025021433 86400 7200 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0