mail.sky.cz has no MX records.
Question and response
Question
dig mail.sky.cz. MX
Answer
The response has no answer records.
Authority
sky.cz. 3600 SOA ns1.poda.cz. hostmaster.poda.cz. 2026010802 10800 3600 2529000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0