How can I preview attachments in Microsoft Office Outlook 2007?

Q: How can I preview attachments in Microsoft Office Outlook 2007?

A: Outlook 2007 lets you preview attachments directly in the preview pane or the body of an open message. This feature has multiple benefits: Workstation and network security are improved, and user efficiency is increased. When you click an attachment to a message, you see a prompt in the preview pane for displaying the attachment’s contents, as Figure 1 shows. If you click the Preview file button, the attachment displays in the preview pane, as Figure 2 shows. If you click an attachment and the extension isn’t associated with a preview handler, you’ll see a message in the preview pane that says “This file cannot be previewed because there is no previewer installed for it.” You’ll also see a link that you can click for more information about Outlook 2007 preview handlers. New Outlook 2007 preview handlers are constantly being developed. For example, Adobe recently added the previewer functionality, which is available to Outlook 2007 when Adobe Reader 8.1 or later is installed.

The attachment preview feature is enabled by default. To disable the feature, select Tools, Trust Center; then open the Attachment Handling section, as Figure 3 shows, and select the Turn off Attachment Preview check box. You can use Group Policy or the Office Customization Tool (OCT) to enable this setting for administrative deployments or changes. You can also manually configure the registry subkey that controls this setting (e.g., through distribution of a .reg file). To disable the attachment preview feature when you next restart Outlook 2007, go to the HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Preferences\DisableAttachmentPreview registry subkey and set the DWORD value to 1.

Outlook 2007’s Trust Center includes an option for listing installed preview handlers. In the Attachment Handling section, click Attachment and Document Previewers. A dialog box similar to the one that Figure 4 shows will open. You can enable or disable various previewers for Outlook 2007 email accounts in this dialog box. The list of disabled items is also stored in the HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Resiliency\DisabledItems registry subkey.

From a security standpoint, using Outlook 2007’s attachment preview is safer than using the associated application to open an attachment. Any malware or script code that’s embedded in an attachment is likely directed at weaknesses in the application expected to open the attachment. The preview pane doesn’t let scripts execute. Thus, if an infected attachment makes it past server and local filtering, the attachment preview reduces the risk of infection that occurs if an attachment is opened with its intended application.

An application’s preview handler status is maintained in the HKEY_CLASSES_ROOT registry subtree. However, editing this subtree to manipulate preview handlers isn’t a user-friendly solution. Stephen Toub, Technical Editor for MSDN Magazine, wrote an application called the Preview Handler Association Editor ( that parses the HKEY_CLASSES_ROOT registry subtree and compiles a list of attachment extensions that you can preview in Outlook 2007.

The previewer technology isn’t solely a component of Outlook. Outlook 2007 and Windows Vista subscribe to the same preview mechanism. Preview handlers are hosted applications that present read-only previews of content to their host. Hosts currently include Outlook 2007 and Microsoft Internet Explorer (IE) in Vista. Third-party software companies can use Microsoft-provided tools to add their documents to the list of attachments that can be previewed in Outlook 2007. For more information about Preview Handlers, see the Microsoft Windows Software Development Kit for Windows Vista and .NET Framework 3.0 Runtime Components Web site ( and the MSDN Preview Handlers Web site (

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