Error message when you click a message attachment in Outlook Web Access after you apply Exchange 2000 Server SP2: "This attachment must be saved to disk"

When you click a message attachment to open it in Microsoft Outlook Web Access (OWA), you receive the following error message:You expect a dialog box that has the following command buttons to appear:

• Open
• Save
• Cancel
• More Info

You experience this behavior after you apply Microsoft Exchange 2000 Server Service Pack 2 (SP2) to the Outlook Web Access server.

This issue occurs because of security changes in Exchange 2000 Server SP2. After you apply Exchange 2000 Server SP2, you receive the error message that is mentioned in the "Symptoms" section when you try to open many kinds of files in Outlook Web Access. For example, you receive this error message when you try to open files that have the following file name extensions:

• .xls
• .doc
• .pdf
• .exe

Note You can open text files (.txt) in Outlook Web Access.

This functionality was included with Exchange 2000 Server SP2 to help enhance security in Exchange. This functionality is intended to help reduce the risk of users running content that the Exchange content engine cannot filter.

This functionality is controlled by the following two registry entries:

• Name: Level2FileTypes
  Value type: REG_SZ
  Value data: file name extensions
• Name: Level2MIMETypes
  Value type: REG_SZ
  Value data: MIME types

These registry entries are located in the following registry subkey:

Warning This workaround may make your computer or your network more vulnerable to attack by malicious users or by malicious software such as viruses. We do not recommend this workaround but are providing this information so that you can implement this workaround at your own discretion. Use this workaround at your own risk.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

You may have a situation in which you do not want users to have to save the message attachment to the local hard disk to view the contents of the message attachment. This might include a situation in which the message attachment contains sensitive company information that may be unintentionally left on the computer on which the message attachment was saved.

To remove the requirement that Outlook Web Access users must save the message attachments to the local hard disk, remove the Level2FileTypes registry entry and the Level2MimeTypes registry entry. To do this, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWEB\OWA
3. On the Registry menu, click Export Registry File.
4. In the File name box, type exported OWA key, and then click Save.
5. In the right pane, right-click Level2FileTypes, and then click Delete. Then, click Yes to confirm the removal of this registry entry.
6. Right-click Level2MIMETypes, and then click Delete. Then, click Yes to confirm the removal of this registry entry.
7. Exit Registry Editor.

After you remove these registry entries, Outlook Web Access users no longer have to save many kinds of message attachments to the hard disk to view them. However, Outlook Web Access users must still save executable files (.exe) to the hard disk.