It is possible to open your own mailbox and, with sufficient permissions, to open another recipient’s mailbox. The owner of a mailbox (a user or an application) has automatic Owner privilege on that mailbox and can therefore open the mailbox and its contents. The owner of a mailbox can assign any of several types of delegate access for that mailbox to another recipient, who can then manipulate the mailbox and its contents according to certain rules.
An owner can also assign access control list (ACL) entries to server store folders, although an ACL entry is not necessary for Owner privileges. A third means of opening mailboxes is a mechanism called privileged access, which is associated with an administrator privilege granted to a server application. Such an application is known as a privileged service.
For more information about delegate access, see Setting Access Controls and DelegateName. For more information about privileged access, see Running an Application as a Privileged Service. For information about ACLs, see About Access Control Lists.