FEATURE: Add rejection message on rejected IncomingEmail

FIX: Better RateLimit description in rejected IncomingEmail
FEATURE: Send email when hitting a rate limit

app/controllers/admin/email_controller.rb

@@ -47,7 +47,7 @@ class Admin::EmailController < Admin::AdminController
 
   def handle_mail
     params.require(:email)
-    Email::Receiver.new(params[:email]).process
+    Email::Receiver.new(params[:email]).process!
     render text: "email was processed"
   end