mail.rightside.ru has no MX records.
Question and response
Question
dig mail.rightside.ru. MX
Answer
The response has no answer records.
Authority
rightside.ru. 1400 SOA ns.rightside.ru. root.rightside.ru. 2025121021 10800 3600 604800 1400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0