cloudrelay01.icewarp.com has no CNAME records.
Question and response
Question
dig cloudrelay01.icewarp.com. NS
Answer
The response has no answer records.
Authority
icewarp.com. 2341 SOA ns1.websupport.cz. admin.websupport.cz. 1772625178 7200 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0