s3-3-w.amazonaws.com has no MX records.
Question and response
Question
dig s3-3-w.amazonaws.com. MX
Answer
The response has no answer records.
Authority
s3-3-w.amazonaws.com. 14341 SOA ns-1425.awsdns-50.org. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 293
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0