delegate

Delegates of shared accounts who can send mail on behalf of and have full control of all the folders in the shared account can save sent items and deleted items in the mailbox owner's folders.

There are two ways to give other users the ability to "send as" another user, mailbox, or public folder address when you use Microsoft Exchange server. The first is using the Delegates feature on the Tools, Options menu. This is configurable in Microsoft Outlook by any user and adds "on behalf of" to the From  

How to display Microsoft Exchange server Public folders and shared Contact folders as Outlook Address Books.