smtp4.ceznet.cz has no MX records.
Question and response
Question
dig smtp4.ceznet.cz. MX
Answer
The response has no answer records.
Authority
ceznet.cz. 300 SOA ns10.cez.cz. netmaster.cezdata.cz. 2025101501 28800 7200 864000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0