mail.cloud.rt.ru has no MX records.
Question and response
Question
dig mail.cloud.rt.ru. MX
Answer
The response has no answer records.
Authority
mail.cloud.rt.ru. 300 SOA ns5.o7.com. admin.o7.com. 1 600 10800 2419200 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0