Q: How do I disable COM add-ins in Microsoft Outlook 2007?

A: Sometimes you need to disable the COM add-ins that are installed with Outlook 2007. For example, when you’re trying to troubleshoot problems such as poor performance, slow shutdown, or even application failure (i.e., crashes), it’s best to eliminate variables. After a crash or hang, Outlook might display a dialog box, such as the one that Figure 1 shows, informing you that a specific add-in is causing problems.

Some add-ins don’t activate until the user tries close the application. An example is the Personal Folders Backup add-in, which prompts the user to back up PST files before closing Outlook. (Ironically, someone developed an add-in that helps Outlook shut down more efficiently. For more information, see http://www.daveswebsite.com/software/olshutdown/index.shtml.)

Disabling COM add-ins prevents them from starting when Outlook starts the next time, which brings Outlook closer to its basic installation and thus allows more control in troubleshooting. The add-ins remain disabled until you re-enable them.

Outlook 2007 has a command-line switch called /noextensions that lets Outlook open without any add-ins. Although the add-ins aren’t disabled in this case, they aren’t loaded with Outlook.

In some cases you know that a specific installed COM add-in (whether from a third party or developed inhouse) is causing problems for your Outlook users. You need to disable such add-ins immediately, until you can find a fix.

In Outlook 2007, you can access add-in management in the new Trust Center, under the Tools menu. Figure 2 shows the Add-in page with several popular add-ins installed, including Acrobat, SnagIt, Xobni, and IntraVNews. Unfortunately, this interface isn’t as intuitive as it could be. The columns in the main Add-ins pane, entitled Name, Location, and Type, aren’t adjustable in width. You can stretch the main window itself to expose the content in the columns, which is especially useful for the Location column. Although you can select an add-in listed in the main window, to make changes to an add-in you must select COM Add-ins from the drop-down box in the Manage section at the bottom of the pane, then click Go. The window that Figure 3 shows will open, allowing selection and deselection of available COM add-ins—which essentially enables or disables the add-ins. Note that clicking the Remove button in Figure 3 will remove the add-in from the list without a warning. Making changes to some add-ins takes effect immediately, whereas an Outlook restart is required for changes to other add-ins.

Outlook might also identify an add-in as problematic and disable it automatically. To view disabled items, as Figure 4 shows, go to the Trust Center’s Add-ins window and select Disabled Items next to the Manage option, then click Go.

You can also enable or disable add-ins through the registry. If Outlook crashes when you try to disable add-ins through the Trust Center, you must use the registry. When a developer creates a COM add-in, the add-in can be registered for all users or just the current user. Outlook add-ins are located in the HKEY_CURRENT_USER\ SOFTWARE\Microsoft\Office\Outlook\Addins registry subkey and the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins registry subkey. The individual available add-ins are listed in the Addins subkeys. Within each Add-ins subkey is a property called LoadBehavior. This property has two possible values: 2 to disable or disconnect the add-in and 3 to enable the add-in. Figure 5 shows this registry value for the OutlookSpy add-in, which is currently disabled.

If you’ve pushed an add-in out to your Outlook clients but the add-in is creating problems, you’ll need to disable it. Because you can disable add-ins through the registry, you can distribute the change through Group Policy Objects (GPOs), a logon script, or another management and distribution mechanism. You can also enable or disable COM add-ins programmatically, through the GenerateOfficeAddInManifest.LoadBehavior property. For information about this process, see http://msdn.microsoft.com/en-us/library/microsoft.visualstudio.tools.office.buildtasks.generateofficeaddinmanifest.loadbehavior.aspx.