In Microsoft Exchange Server 2019 or Exchange Server 2016, a user might have two Windows accounts, one without a mailbox (for example, this is used for administrative purposes), let's call this WindowsOnlyAccount and a standard mailbox account to which an AddressBookPolicy is applied. When the WindowsOnlyAccount is currently logged on, the user can create an Outlook online-mode profile and provide the credentials of the mailbox account. In this scenario, address list separation isn’t applied any longer for this mailbox user. This results in all address lists being visible and browsable. That means:
- All address book information about the exchange organization can be viewed if the user has full permissions to another user's mailbox.
- All address book information about the exchange organization can be viewed until Outlook is started at least a second time if the user uses another user's credentials to sign in to his mailbox.