Answer by flip for Windows Server 2019 built-in SMTP server: Emails stuck in queue and "The remote server did not respond to a connection attempt" in event log

Just leaving this here for posterity after one of my engineers spent hours on it while setting it up on Windows Server 2022 with AWS SES and getting the same error message:Event 4006, smtpsvc

1. Make sure the AWS credential was created on the same region that you specify on the Advanced -> smart host .
2. If you are testing by dropping a manually created file on pickup folder, make sure it has this structure (note the extra line between subject and body):

from:from@address.com
to:to@address.com
subject:testing

This is the test message body.