mx.ptl.ru has no CNAME records.
Question and response
Question
dig mx.ptl.ru. NS
Answer
The response has no answer records.
Authority
ptl.ru. 9564 SOA ns.quantum.ru. admin.quantum.ru. 202438349 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0