Trying to set up reply by email: ActionController::RoutingError (No route matches [POST] "/admin/email/handle_mail")

Stopped getting above error (no route matches), but still getting 400. Not fixed, apparently can’t do easily with mailgun, there’s a plugin but it’s broken.

Maybe AWS SES & Lambda? I don’t understand, it seems like this should be a pretty darn standard feature, why is it so hard to find a simple tutorial?

There aren’t even any docs I can find explaining the format of the HTTP POST request to send to admin/email/handle_mail. Just this topic which is not explicit at all.