ns4.dhub.ru has no MX records.
Question and response
Question
dig ns4.dhub.ru. MX
Answer
The response has no answer records.
Authority
dhub.ru. 3600 SOA ns3.dhub.ru. administrator.dhub.ru. 357 900 600 86400 3600
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0