It's not uncommon to see that mailboxes contain sensitive information or company-internal documents that possibly include personal, financial, or other private records of third-party individuals or companies.

Especially in larger environments it's difficult to keep track of who has access to what, even more so it's almost impossible to track who exercised the permissions that he or she was granted.

Mailbox audit logging will exactly do that: keep track of who accesses a mailbox. Not only will it do that for users or delegates, but also for administrators. The latter would not only happen when an Administrator opens another user's mailbox, but also when administrative tasks are executed like In-Place eDiscovery or Mailbox Export Requests.