mailer01.send-box.ru has no CNAME records.
Question and response
Question
dig mailer01.send-box.ru. NS
Answer
The response has no answer records.
Authority
send-box.ru. 300 SOA ns1.mail.ru. hostmaster.mail.ru. 3491252382 3600 900 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0