mx.INFRAMX.RU has no CNAME records.
Question and response
Question
dig mx.INFRAMX.RU. NS
Answer
The response has no answer records.
Authority
INFRAMX.RU. 15 SOA ns5.o7.com. admin.o7.com. 24 600 10800 2419200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0