yaroslavl.su has no MX records.
Question and response
Question
dig yaroslavl.su. MX
Answer
The response has no answer records.
Authority
yaroslavl.su. 86400 SOA ns.innet.yaroslavl.su. hostmaster.innet.yaroslavl.su. 2005091383 86400 1800 604800 86400
Additional
. 0 OPT [{Extended_DNS_Error: PROHIBITED}] ; payload 1232, xrcode 0, version 0, flags 0