smtp.t-email.cz has no MX records.
Question and response
Question
dig smtp.t-email.cz. MX
Answer
The response has no answer records.
Authority
t-email.cz. 3600 SOA idunn.t-mobile.cz. dss-system.t-mobile.cz. 1772707817 43200 1850 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0