mail.happysrv.de has no CNAME records.
Question and response
Question
dig mail.happysrv.de. NS
Answer
The response has no answer records.
Authority
happysrv.de. 3546 SOA root-dns.netcup.net. dnsadmin.netcup.net. 2026030805 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0