MIgration of Lotus Notes mail to Microsoft outlook but keeping lotus notes based applications

Our Company will be migrating the Domino mail server to Microsoft Exchange but will be retaining our Lotus Notes Client based applications (e.g. Leave application , etc) and I have a few concerns about this.

1 . For Domino Directory I assume the we need to keep it so that the user can still create new application as well as access the old one. Right?

  1. When creating a new application ( leave application) in lotus notes when I click submit, how will the Application will directly goes to Outlook mail instead of Lotus Notes mail?

  2. For this do we need to keep two Address book one for Domino and one for Microsoft exchage?

  3. How domino application server and Microsoft excahnge will communicate?

Please need your advise.