ns.belleville.cz has no MX records.
Question and response
Question
dig ns.belleville.cz. MX
Answer
The response has no answer records.
Authority
belleville.cz. 2560 SOA ns1.websupport.cz. admin.websupport.cz. 1757172707 7200 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0