smtp.mastertelecom.ru has no MX records.
Question and response
Question
dig smtp.mastertelecom.ru. MX
Answer
The response has no answer records.
Authority
mastertelecom.ru. 3600 SOA ns1.mastertel.ru. noc.mastertel.ru. 2024122300 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0