ns4.centralnic.net has no MX records.
Question and response
Question
dig ns4.centralnic.net. MX
Answer
The response has no answer records.
Authority
centralnic.net. 300 SOA ns0.centralnic.net. hostmaster.centralnic.net. 2025011534 3600 60 6048000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0