spf.mindbox.ru has no MX records.
Question and response
Question
dig spf.mindbox.ru. MX
Answer
The response has no answer records.
Authority
mindbox.ru. 300 SOA ns1.edgedns.co. support.edgecenter.ru. 1771787648 5400 3600 1209600 300
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0