The Grant Admin Consent page of the Configure Office 365 Mailbox Access Wizard allows you to grant admin consent for the full_access_as_app permission to the Out-of-Office Extender app, which is required the to access mailboxes.
When you are ready, click the Next button.
You will be prompted consent to permissions required by the Out-of-Office Extender app:
Once admin consent has been granted, the wizard moves to the Certificate page.