In Outlook, you may give permission to others to access your e-mail folders. The following is an example of how user A allows user B to open the 'Inbox' folder of user A.

In user A's account, assign permissions to user B

1. Login using Outlook as user A.
2. In the Folder list, right-click A's Mailbox folder and select Properties
3. Click the Permissions tab.
4. Click on the Add button.
5. Select the name of User B from the list shown in the left panel and click Add. Click OK when finished.
6. Back to the previous window, select the name of user B under the Name field.
7. Under Permissions, either choose a role or check appropriate permissions.
8. Click OK.
9. Right-click A's Inbox folder and select Properties.
10. Repeat the steps from 2 to 8.

In user B's account, open the mailbox of user A

1. Login using Outlook as user B.
2. On the Tools menu, choose Services.
3. Click Microsoft Exchange Server in the Services list, and click Properties.
4. On the Advanced tab, click Add.
5. Type the e-mail account name of user A in Add Mailbox.
6. Click OK.

Note: By doing the above, user B can only open Inbox of user A. If user B needs to open other mail folders of user A, user A has to assign the appropriate permissions to user B for each folder one by one.