Article ID: 960250
On a computer that has Microsoft Office Outlook 2003 installed, external content is always blocked for attached e-mail messages after you install security update 949031 (security bulletin MS08-015).
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
To resolve this problem, apply hotfix package 959628, and then configure the DisableSenderTypeSecurity registry entry to enable the hotfix package. To do this, follow these steps:
For most external content, Outlook checks the sender type of the e-mail messages as part of the test for whether to show the contact. E-mail messages from an internal sender are considered safe. Therefore, external content is allowed. Security update 949031 changed this behavior for attached e-mail messages and file system based e-mail messages. With that update applied, the external content is blocked regardless of the sender type. This hotfix, together with the registry value, adds the sender test back. Therefore, if the e-mail message is from an internal sender, the external content is downloaded successfully. The new registry value actually disables the bypassing of the sender type. Therefore, the name of the registry entry is somewhat misleading. By setting the value, you tell Outlook to include the sender type in the test for safety for these kinds of messages.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
(http://go.microsoft.com/fwlink/?LinkId=151500)for other considerations.