Known issues in Outlook 2010 when you develop custom solutions

This article provides an overview of some known issues that occur with the Microsoft Outlook 2010 development platform. The known issues that are mentioned in this article are not directly related to the object model, to Outlook 97-2003 custom forms, or to the form regions that were introduced with Microsoft Office Outlook 2007. This is because these issues are covered in other Microsoft Knowledge Base articles that are listed in the "Related Microsoft Knowledge Base articles" section.

This article discusses some known issues when you develop custom solutions for Outlook 2010.

How to enable the Developer tab

By default, the Developer tab in the Fluent Ribbon is not enabled. However, this tab provides many features for developers. To enable the Developer tab in Outlook 2010, follow these steps:

1. On the File menu, click Options.
2. Click the Customize Ribbon category.
3. In the list of Main Tabs, click to enable Developer and then click OK.

How to locate the Disabled Items command

To access the Disabled Items dialog box, use one of the following methods.

Method 1

If you have enabled the Developer tab, click the Disabled Items button on the ribbon.

Method 2

1. On the File menu, click Options.
2. In the Navigation Pane, click Add-ins.
3. In the Manage list, select Disabled Items, and then click Go.

Accessing security settings for custom form scripts

To access the Allow script in shared folders option and the Allow script in public folders option in Outlook 2010, follow these steps:

1. On the File menu, click Options.
2. In the Navigation Pane, click Trust Center, and then click the Trust Center Settings button.

Notice that the Allow script in shared folders option and the Allow script in Public Folders option are located under Script in Folders.

The DontDisplayHKLMAddins registry entry hides COM add-ins

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:
In Outlook 2010, you can use the DontDisplayHKLMAddins registry entry to hide COM add-ins that are registered under the HKEY_LOCAL_MACHINE key. When you hide these COM add-ins, users cannot unload them. When you enable the DontDisplayHKLMAddins registry entry, Outlook 2010 has the same behavior as Microsoft Office Outlook 2000, Microsoft Office Outlook 2002, and Microsoft Office Outlook 2003.

To add the DontDisplayHKLMAddins registry entry for Outlook 2010, follow these steps:

1. Click Start , click Run , type regedit in the Open box, and then click OK.
2. Locate and then right-click the following subkey:
   HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security
3. Point to New, and then click DWORD Value.
4. Type DontDisplayHKLMAddins, and then press ENTER.
5. Right-click DontDisplayHKLMAddins, and then click Modify.
6. In the Value Data box, type 1 to hide the COM add-ins that are registered under the HKEY_LOCAL_MACHINE key, and then click OK.
   Note If you type 0 in the Value Data box, or if you leave the Value Data box empty, the COM add-ins are displayed.
7. Exit Registry Editor, and then restart the computer.

When the DontDisplayHKLMAddins registry entry is equal to 1, all COM add-ins are still displayed in the Trust Center. This registry setting hides HKLM-registered COM add-ins only in the COM Add-Ins dialog box. This should be acceptable because you can only load and unload the add-ins by using the COM Add-Ins dialog box.

The DisableCreateServices registry entry prevents specific MAPI services from loading

An administrator can create the DisableCreateServices registry entry under the following subkey: This registry entry was new in Outlook 2007. You can use the DisableCreateServices registry entry to prevent specific MAPI services from loading.

The DisableCreateServices registry entry stores a string value. The string value is a semicolon-delimited list of MAPI services. The names of the services are the MAPI names that appear in the Mapisvc.inf file. For example, if the following is a subset from a Mapisvc.inf file, you can use a string value of MSOMS;OMSAB in the DisableCreateServices registry entry to prevent users from adding these two services:
In the context of custom solutions, developers should be aware that organizations can now deploy policies that may restrict using a MAPI service.

Custom properties may not propagate in some scenarios

The AllowNamedProps registry key was introduced in Microsoft Office Outlook 2003 Service Pack 2 (SP2). This key stores a list of custom properties that you can use in Outlook. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
Microsoft Knowledge Base article 907985 also describes the following registry keys:

• AllowTNEFtoCreateProps
• AllowMSGFilestoCreateProps
• DisallowTNEFPreservation

These three registry keys are not supported in Outlook 2010.

Outlook Today is being deprecated

Developers are encouraged not to customize the Outlook Today page. This feature is being deprecated. It is being maintained only for backward-compatibility reasons.

Collaboration Data Objects 1.2.1 is not supported with Outlook 2010

Collaboration Data Objects (CDO) 1.2.1 is a downloadable package that provides access to Outlook-compatible objects through a COM-based API. CDO was available as a download for Outlook 2007. But CDO 1.2.1 is no longer supported for use with Outlook and Outlook’s client-side implementation of MAPI. Instead of using CDO 1. 2.1, developers are encouraged to use the Outlook object model if they can use that model.

How to create preview handlers for Outlook attachments

Outlook 2010 lets you preview certain kinds of attached files when you are viewing e-mail messages. Outlook and other applications in Microsoft Office 2010 use the same API architecture that was first available with Windows Vista. For information about how to create a preview handler, visit the following Microsoft Developer Network (MSDN) website:By default, MAPI forms do not open

By default, and like Outlook 2007, Outlook 2010 does not open MAPI forms that were created by using C++. To enable this functionality, follow these steps:

1. On the File menu, click Options.
2. In the navigation pane, click Advanced.
3. Under Developer, click Custom Forms.
4. Click to select the Allow forms that bypass Outlook check box.

BUG #: 402066 (Office12)

By default, COM add-ins that are registered in the HKEY_LOCAL_MACHINE key are no longer hidden

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: COM add-ins can be registered in either the HKEY_CURRENT_USER key or the HKEY_LOCAL_MACHINE key. In earlier versions of Office, add-ins that are registered in the HKEY_CURRENT_USER key appear in the COM Add-ins window. However, add-ins that are registered in the HKEY_LOCAL_MACHINE key do not appear in the COM Add-ins window. This behavior lets developers and administrators register an add-in in the HKEY_LOCAL_MACHINE key so that users cannot remove the add-in.

The 2007 Microsoft Office system changes this default behavior. The Trust Center and the COM Add-ins window list all registered add-ins. If administrators want to hide add-ins that are registered in the HKEY_LOCAL_MACHINE key, they can deploy a policy key to enable the earlier behavior.

To hide add-ins that are registered in the HKEY_LOCAL_MACHINE key, follow these steps:

1. Click Start , click Run , type regedit in the Open box, and then click OK.
2. Locate and then right-click the following subkey:
   HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security
3. Point to New, and then click DWORD Value.
4. Type DontDisplayHKLMAddins, and then press ENTER.
5. Right-click DontDisplayHKLMAddins, and then click Modify.
6. In the Value Data box, type 1 to hide the add-ins that are registered in the HKEY_LOCAL_MACHINE key, and then click OK.
7. Exit Registry Editor, and then restart the computer.

Outlook 2010 no longer supports Exchange client extensions

The Microsoft Exchange client extension (ECE) architecture was originally supported by the Exchange Server client in Microsoft Windows 95 and was also supported by Outlook 97 through Outlook 2007. Outlook 2010 no longer supports ECEs. Instead, developers should implement a COM add-in for Outlook 2010.

Visual Basic Editor settings may not be preserved

If you change settings in the Microsoft Visual Basic Editor, such as to show or hide windows that are displayed, those settings may not persist when you exit Outlook. For more information, click the following article number to view the article in the Microsoft Knowledge Base: Related Microsoft Knowledge Base articles

For the Outlook 2007 version of this article, click the following article number to view the article in the Microsoft Knowledge Base: For similar articles that cover issues with other aspects of the Outlook 2010 development platform, click the following article numbers to view the article in the Microsoft Knowledge Base