Choose: File > Account Settings > Delegate Access
Figure 1: Delegate access command
Click Add (to remove a delegate, simply click on the delegates name and press Remove)
Figure 2: Delegates dialog
Chose the person you wish to grant permission to from the GAL (Global Address List)
Figure 3: Address book, select delegates
Click Add and OK.
In the Delegate Permissions window, specify the access you would like to grant the delegate(s)Here you can specify access to all of your Mail Folders. If you wish for the user to only have access to certain things specify this here.
Figure 4: Delegate permissions settings
Notice you can opt to send a notification to the user you are delegating permissions to, and you can also grant access to your private items.
Click OK to save changes and close the Delegate Permissions window