ns4.s7host.net has no MX records.
Question and response
Question
dig ns4.s7host.net. MX
Answer
The response has no answer records.
Authority
s7host.net. 3600 SOA ns1.s7host.net. admin.sencia.ca. 2026010101 900 600 43200 3600
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0