winserver.icewarp.com has no CNAME records.
Question and response
Question
dig winserver.icewarp.com. NS
Answer
The response has no answer records.
Authority
icewarp.com. 1366 SOA ns1.websupport.cz. admin.websupport.cz. 1772468836 7200 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0