sandbox.webkomplet.cz has no MX records.
Question and response
Question
dig wkvm01.webkomplet.cz. MX
Answer
The response has no answer records.
Authority
webkomplet.cz. 360 SOA ns1.ignum.com. hostmaster.ignum.cz. 2026030401 10800 3600 604800 360
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0