aws has no MX records.
Question and response
Question
dig aws. MX
Answer
The response has no answer records.
Authority
aws. 60 SOA dns1.nic.aws. hostmaster.nominet.org.uk. 1767917929 900 300 2419200 60
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0