According to this, it sounds like the setting is for Discourse learning about bounces that were received by Amazon after sending via SES.
However, I’m using SES just to send messages for forum.example.com, and I’m using mail-receiver to receive replies and bounces. I think the warning message in the Discourse dashboard only applies to people receiving replies & bounces via SES, right? Not for those with an MX record going to our own server?