ns8.strongns.net has no MX records.
Question and response
Question
dig ns8.strongns.net. MX
Answer
The response has no answer records.
Authority
strongns.net. 3601 SOA freedns1.registrar-servers.com. hostmaster.registrar-servers.com. 1580224564 43200 3600 604800 3601
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0