Outlook 2007 provides tremendous functionality right out of the box and could well serve all your needs. However, if you need additional features not provided directly by Outlook 2007, add-ins can help to extend Outlook 2007 functionality. Outlook 2007 includes a handful of such add-ins, and third-party developers can produce others.

Outlook 2007 supports two types of add-ins: application-specific (standard) add-ins and Component Object Model (COM) add-ins. Standard add-ins are the type supported by earlier versions of Microsoft Outlook, which allow a developer to add features to one Microsoft Office system application. Standard add-ins are not portable between Microsoft Office system applications. These add-ins are integrated into Outlook 2007 through dynamic-link libraries (DLLs).

COM add-ins use the Microsoft COM to allow shared functionality between the various Microsoft Office system applications. COM add-ins were added as new features in Microsoft Office 2000 and are therefore also available in Microsoft Office 2003 and Outlook 2007. These add-ins are integrated into Microsoft Office system applications, including Outlook 2007, through either DLLs or ActiveX^® controls.

You install add-ins when you install the Microsoft Office system; the list of available add-ins depends on which options you select during installation. To view the installed add-ins, choose Tools, Trust Center, and then click the Add-Ins link. Click the drop-down list next to Manage. Choose Exchange Client Extensions to view, install, and enable or disable standard Outlook 2007 add-ins, and click COM Add-Ins to view, install, and enable or disable COM add-ins and control their loading behavior. With your choice selected, click Go to manage the settings.