smtp.starnet.cz has no MX records.
Question and response
Question
dig smtp.starnet.cz. MX
Answer
The response has no answer records.
Authority
starnet.cz. 3600 SOA ns1.starnet.cz. radek.krejca.starnet.cz. 2026022102 3600 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0