Yes, for that first fix the oob setup as it is shared across the board.
This will answer this question. (and the duplicate question you have created that too)
Now for the client requirement you can create a new email and along with it a new inbound email action as well to cater for the new requirements. This way you don't alter the OOB behavior and create one separately for problem. You can refer to the existing code for that or raise a new question here on community also.
Hope this helps.
-Anurag
