mail.webstep.cz has no CNAME records.
Question and response
Question
dig mail.webstep.cz. NS
Answer
The response has no answer records.
Authority
webstep.cz. 600 SOA ns.webstep.cz. root.webstep.net. 2026022301 14400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0