pdx-out-007.esa.us-west-2.outbound.mail-perimeter.amazon.com has no AAAA records.
Question and response
Question
dig pdx-out-007.esa.us-west-2.outbound.mail-perimeter.amazon.com. AAAA
Answer
The response has no answer records.
Authority
us-west-2.outbound.mail-perimeter.amazon.com. 900 SOA ns-904.awsdns-49.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0