mail.luminet.cz has no MX records.
Question and response
Question
dig mail.luminet.cz. MX
Answer
The response has no answer records.
Authority
luminet.cz. 10800 SOA ns1.grapesc.cz. domeny.grapesc.cz. 2025270503 10800 3600 1209600 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0