mail.cloudcamp.cz has no CNAME records.
Question and response
Question
dig mail.cloudcamp.cz. NS
Answer
The response has no answer records.
Authority
cloudcamp.cz. 894 SOA ns1.geetoo.com. hostmaster.geetoo.com. 15 1200 600 1209600 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0