Currently when Domino server is configured with Smarthost, so Domino will send the message to Smarthost if the user is not found in Domino directory. Now some customers have requirement to forward the message again from Smarthost to Domino directory especially when 2 companies have merged.
If the user is not present in Smarthost also and Smarthost again sends this message to Domino then Domino will again send it to Smarthost. This essentially creates a loop between Domino and Smarthost and finally the error comes as "Messages probably in routing loop, fixed maximum hop count exceeded.".
So for incorrect address mail, the mail loops and gives this error to sender. So sender has no way to understand that user address was incorrect. So there is a feature request to add the internal counter when the same message is forwarded to Smarthost multiple times. This can be done using message ID. So if the message is returned from Smarthost to Domino then Domino should send the DFR saying "User not found in Directory". This will not only avoud looping but also give proper DFR to sender.