ns4.mts-ws.net has no MX records.
Question and response
Question
dig ns4.mts-ws.net. MX
Answer
The response has no answer records.
Authority
mts-ws.net. 900 SOA ns2.mts.ru. dns.mts.ru. 2026021901 10800 1800 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0