rez2.oxit.cz has no MX records.
Question and response
Question
dig rez2.oxit.cz. MX
Answer
The response has no answer records.
Authority
oxit.cz. 38400 SOA shinzon.blueboard.cz. hostmaster.blueboard.cz. 2017072562 10800 3600 604800 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0