core2.obtelecom.ru has no MX records.
Question and response
Question
dig core2.obtelecom.ru. MX
Answer
The response has no answer records.
Authority
obtelecom.ru. 3600 SOA ns.obcity.ru. dennsk.gmail.com. 2016070416 3600 900 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0