mx.simply.com has no CNAME records.
Question and response
Question
dig mx.simply.com. NS
Answer
The response has no answer records.
Authority
simply.com. 3483 SOA ns1.simply.com. hostmaster.simply.com. 2026022000 14400 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0