mail.ry.cz has no MX records.
Question and response
Question
dig mail.ry.cz. MX
Answer
The response has no answer records.
Authority
ry.cz. 1800 SOA ns.gransy.com. root.gransy.com. 2753303420 86400 900 1209600 1800
mail.ry.cz. 1800 NSEC mesos.ry.cz. A RRSIG NSEC
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0