rostov-vr.smartspb.net has no MX records.
Question and response
Question
dig rostov-vr.ra.smartspb.net. MX
Answer
The response has no answer records.
Authority
smartspb.net. 600 SOA ns4.smartspb.net. hostmaster.smartspb.net. 930 28800 1800 1209600 28800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0