To do this you will need to give them reviewer access to mailbox first, then
grant them the necessary permission to the sent items folder. Here are the
instructions.
In the Folder List, right-click "Outlook Today - [Mailbox - Your Mailbox]"
select Properties and click the Permissions tab. Grant them at least the
Reviewer role.
In the Folder List, right-click the "Sent Items" folder click Properties
then click the Permissions tab. Assign them the role of your choice.
Now, the person whom you have granted access to the Sent Items folder will
need to add the mailbox to their folder list. Within Outlook they need to go
to Tools, Email Accounts, click Next, click Change, click More Settings,
click the Advanced tab and add the mailbox by clicking Add.
