How to Assign Application Impersonation role?
The Application Impersonation role enables the application to impersonate users in an organization in order to perform tasks on behalf of the user. Here are the steps, to assign this role for a user:
1. Log on to your Exchange Admin Center.
   
2. Click on “Permissions” in the left pane and then click on “New” button in the Admin Roles tab for adding a new role group.
 
   
3. In the “new role group” window, give a unique name for role group in the Name field.
 
   
4. In the field given for roles, click on ‘Add’ button and select ‘ApplicationImpersonation’ from the list of available roles.
 
   
5. Add members, in the field given for the users, you wish to assign this role.