There are two ways of accessing a mailbox you have full access to. One of the methods is to open only the particular folder you wish to view, such as inbox, or contacts. This can be achieved by selecting Open > Other User's Folder and following the instructions, this method allows multiple folders to be set up within your Outlook client without risking slowness or crashes by having several large mailboxes configured instead.

Alternatively you may open the entire mailbox within your Outlook client. This may slow Outlook's performance slightly and it is not recommended to have a large number of mailboxes under the same Outlook client, as this can cause performance issues and crashes:

1) Open Outlook 2010.

2) Click on file.

3) Under the Info header, click on the Account Settings button and then on the Account Settings tab.

4) Click on Change.

5) Click the More Settings button.

6) Click on the Advanced tab then click on Add.

7) Enter the email address of the delagated mailbox into the Add Mailbox field.

8) Click on Apply and then on OK. Outlook will now be busy accessing the other mailbox’s data, so this may take a while.

9) Back on the Change Account window, click on Next and then on Finish

10) Close the Account Settings window. You should now see both mailboxes in your Outlook profile.