mailer01.proplex.ru has no CNAME records.
Question and response
Question
dig mailer01.proplex.ru. NS
Answer
The response has no answer records.
Authority
proplex.ru. 74 SOA ns3-l2.nic.ru. connect.proplex.ru. 2012041479 14400 3600 2592000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0