smtp0.s7host.net has no CNAME records.
Question and response
Question
dig smtp0.s7host.net. NS
Answer
The response has no answer records.
Authority
s7host.net. 1524 SOA ns1.s7host.net. admin.sencia.ca. 2026022505 900 600 43200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0