delta.sws.cz has no MX records.
Question and response
Question
dig delta.sws.cz. MX
Answer
The response has no answer records.
Authority
sws.cz. 3600 SOA ns.sws.cz. itrubelik.sws.cz. 1154 3600 600 2419200 3600
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0