sip.bisv.ru has no MX records.
Question and response
Question
dig sip.bisv.ru. MX
Answer
The response has no answer records.
Authority
bisv.ru. 10800 SOA ns1.bisv.ru. support.bisv.ru. 2026021201 86400 900 1857600 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0