ints.onet.sk has no MX records.
Question and response
Question
dig ints.onet.sk. MX
Answer
The response has no answer records.
Authority
onet.sk. 2560 SOA ns1.websupport.sk. admin.websupport.sk. 1770971181 7200 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0