mail.sn.ru has no MX records.
Question and response
Question
dig mail.sn.ru. MX
Answer
The response has no answer records.
Authority
sn.ru. 86400 SOA ns5.salenames.ru. noc.salenames.ru. 2025111801 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0