bbcustomer.zsttk.net has no MX records.
Question and response
Question
dig bbcustomer.zsttk.net. MX
Answer
The response has no answer records.
Authority
bbcustomer.zsttk.net. 86400 SOA ns1.zsttk.net. hostmaster.zsttk.ru. 2013071700 43200 3600 2419200 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0