sip.bs.com.ru has no MX records.
Question and response
Question
dig sip.bs.com.ru. MX
Answer
The response has no answer records.
Authority
bs.com.ru. 14400 SOA ns.sco.ru. admin.sco.ru. 2025092901 600 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0