gtspremiumnet.cz has no MX records.
Question and response
Question
dig gtspremiumnet.cz. MX
Answer
The response has no answer records.
Authority
gtspremiumnet.cz. 86400 SOA ns1.gts.cz. hostmaster.cz.net. 2012102900 28800 7200 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0