ex.infobox.ru has no MX records.
Question and response
Question
dig ex.infobox.ru. MX
Answer
The response has no answer records.
Authority
infobox.ru. 600 SOA sns1.rsnx.ru. dnsmaster.infobox.ru. 2025121609 10800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0