core.ttnet.cz has no MX records.
Question and response
Question
dig core.ttnet.cz. MX
Answer
The response has no answer records.
Authority
core.ttnet.cz. 86400 SOA ns.ttnet.cz. hostmaster.ttnet.cz. 2002352066 28800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0