In Office 365 the Impersonation permission allows a service application to impersonate a user account performing operations associated with the impersonated account.
Generally Impersonation is required by some applications that performs operations in Office 365 environment, typically items migration, import or export activities or backup of Office 365 mailboxes.
Access the Office 365 portal by typing in your favorite browser the address https://portal.office.com. Enter the admin credentials and click Sign in.
From the Dashboard menu, select Admin centers > Exchange to access the Exchange admin center area.
Click permissions in the left pane and select, for example, Hygiene Management from the admin roles list (you can also click on Add icon to assign a role for Impersonation). Click the Edit button (pencil icon) to configure the selected role.
From the Hygiene Management screen click Add (plus sign) under Roles section.
Select ApplicationImpersonation from the list and click add -> button. Click OK to confirm.
Then click Add under Members section.
From the list select the user you want to grant Impersonation rights and click add -> button. Click OK to confirm.
Now click Save to save the configuration.
The ApplicationImpersonation rights have been assigned to the selected user.
After assigning the Impersonation permission to the required Office 365 account, applications used to do activities in the Office 365 environment (migrations, export or import tasks for example) can operate properly.