ns4.nasdns.net has no MX records.
Question and response
Question
dig ns4.nasdns.net. MX
Answer
The response has no answer records.
Authority
nasdns.net. 86400 SOA ns10.nasdns.net. nascloud.nadserv.com. 2025081501 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0