ca-central-1.compute.amazonaws.com has no MX records.
Question and response
Question
dig ca-central-1.compute.amazonaws.com. MX
Answer
The response has no answer records.
Authority
ca-central-1.compute.amazonaws.com. 60 SOA ns-924.awsdns-51.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 60
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0