mx1.web4ce.cz has no CNAME records.
Question and response
Question
dig mx1.web4ce.cz. NS
Answer
The response has no answer records.
Authority
web4ce.cz. 7196 SOA ns1.web4ce.cz. domeny.web4ce.cz. 2026030901 28800 7200 1814400 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0