mailbackup.wnhcloudserver.com has no CNAME records.
Question and response
Question
dig mailbackup.wnhcloudserver.com. NS
Answer
The response has no answer records.
Authority
wnhcloudserver.com. 3582 SOA ns39.domaincontrol.com. dns.jomax.net. 2025120100 28800 7200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0