dns4.cz has no MX records.
Question and response
Question
dig dns4.cz. MX
Answer
The response has no answer records.
Authority
dns4.cz. 86400 SOA ns.dns4.cz. hostmaster.active24.cz. 2012121401 10800 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0