ns.0rbitel.net has no MX records.
Question and response
Question
dig ns.0rbitel.net. MX
Answer
The response has no answer records.
Authority
0rbitel.net. 86400 SOA ns.0rbitel.net. root.orbitel.bg. 2018010401 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0