us-west-2.amazonaws.com has no MX records.
Question and response
Question
dig us-west-2.amazonaws.com. MX
Answer
The response has no answer records.
Authority
us-west-2.amazonaws.com. 7200 SOA dns-external-route53.us-east-1.amazonaws.com. root.amazon.com. 1 3600 900 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0