webmail-a.isp.cz.net has no CNAME records.
Question and response
Question
dig webmail-a.isp.cz.net. NS
Answer
The response has no answer records.
Authority
cz.net. 10800 SOA ns.eunet.cz. hostmaster.cz.net. 2025121100 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0