prometheus.zcom.cz has no MX records.
Question and response
Question
dig prometheus.zcom.cz. MX
Answer
The response has no answer records.
Authority
zcom.cz. 1800 SOA ns1.zcom.cz. hostmaster.zcom.cz. 1771887052 10800 3600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0