This feature requires you to be using a Microsoft Exchange Server e-mail account.
The levels of permission that a delegate can be granted are as follows:
Author As a delegate, you can read and create items, and modify and delete items you create. For example, a delegate can create task requests and meeting requests directly in the manager's Task or Calendar folder, and then send either item on the manager's behalf.
Editor As a delegate, you can do everything an Author can do, plus modify and delete the items the manager created.
Reviewer As a delegate, you can read items; for example a delegate with Reviewer permission can read messages in another person's Inbox.
Note With author or editor permissions, the delegate has send-on-behalf-of permission. Sent messages contain both the manager's and delegate's names. Message recipients see the manager's name in the Sent On Behalf Of box and the delegate's name in the From box.
If a delegate needs permission to work with meeting requests and responses only, the manager can select the user on the Delegates tab (Tools menu, Options command), click Permissions, and then select the Delegate receives copies of meeting-related messages sent to me check box. The manager does not need to grant permission to their Inbox. Meeting requests and responses will go directly to the delegate's Inbox. The delegate will, however, need editor permission to the manager's Calendar folder, because once they respond to the meeting on behalf of the manager, the meeting is automatically added to the manager's Calendar folder.