Ah thanks for the topic, this had eluded me. We should have explained when this setting applies and where to find the value, and the warning is too broad.
It appears whenever the SMTP hostname looks like SES and the allowlist is empty, even if SNS isn’t part of your setup.
If SES bounce feedback is reaching Discourse through mail-receiver, you don’t need to populate this setting. You can leave it empty.
@Jonathan5, the bounce topic ARN you added is the right value. Though, small note - Discourse currently only processes bounces through this webhook, so adding the complaint topic doesn’t enable complaint handling.
We’ve updated the descriptions and warnings to indicate as such, so they can be ignored when not applicable. Thanks for the feedback!