Make sure 'expand' is checked and set to 'true', otherwise the service account will not be able to check other mailboxes.

Set up the service account

  1. Log on to the Exchange Admin through the Office365 portal.
  2. In the Exchange admin center, click permissions.
  3. Click (plus) to create a new role group.
  4. Enter a descriptive name in the popup window.
  5. Click on the (plus) to add a role and choose ApplicationImpersonation.
  6. Use (plus) to add the member user you want allow these permissions to.

Use these settings to enter in the manage-sources-email section of Indica.