FEATURE: clearer error message when receiving a reply to an old notification

lib/email/processor.rb

@@ -55,6 +55,7 @@ module Email
                          when ActiveRecord::Rollback                       then :email_reject_invalid_post
                          when Email::Receiver::InvalidPostAction           then :email_reject_invalid_post_action
                          when Discourse::InvalidAccess                     then :email_reject_invalid_access
+                         when Email::Receiver::OldDestinationError         then :email_reject_old_destination
                          else                                                   :email_reject_unrecognized_error
       end
 
@@ -75,6 +76,10 @@ module Email
         Rails.logger.error(msg)
       end
 
+      if message_template == :email_reject_old_destination
+        template_args[:short_url] = e.message
+      end
+
       if message_template
         # inform the user about the rejection
         message = Mail::Message.new(mail_string)