I’m sure that you caught this -> have you verified the outgoing email address that discourse uses to send?
If it is notify@yourverifieddomain, you need to go into SES, second row under ‘Identity Management’ and add then verify the sending email. Nothing goes out until you do this.
No alarms, no sirens, just no go.
Having a gmail reply is great. That is what I did. Then members authorization emails were getting spam blocked because From and Reply didn’t match.
Eventually I wrote a simple AWS Lambda (took a week to learn how) that forwards incoming email to the Discourse API. Very clean. No POSTIX.