ns1.private-nameserver.net has no MX records.
Question and response
Question
dig ns1.private-nameserver.net. MX
Answer
The response has no answer records.
Authority
ns1.private-nameserver.net. 86400 SOA ns1.private-nameserver.net. admin.private-nameserver.net. 2019110701 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0