cz has no MX records.
Question and response
Question
dig cz. MX
Answer
The response has no answer records.
Authority
cz. 900 SOA a.ns.nic.cz. hostmaster.nic.cz. 1771755436 900 300 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0