These you need wen you want more control over Sent Items when using shared mailboxes.
Whether a mailbox is used by multiple users as a communication tool, a shared mailbox remains an important business requirement.
Early releases from Exchange 2013 there was a no way to configure this behavior.
In Office 365 and Exchange 2013 CU9, this feature on shared mailboxes is disabled by default.
If you mis it run:
setup.exe /preparead /iacceptexchangeserverlicenseterms