Support for keeping add-ins enabled
Programs in Office 2013 and later versions provide add-in resiliency, meaning that apps will disable an add-in if it performs slowly. However, you can re-enable add-ins and prevent add-ins from being auto-disabled by other Office programs.
Preventing add-ins from being disabled
While most add-ins will not be disabled by the add-in disabling feature, you don't want your add-in to be disabled consistently.
Following are some suggestions for improving add-in performance:
Prefer native COM add-ins over managed add-ins because managed add-ins must incur the overhead of loading the .NET Framework during Outlook startup.
If you have long-running tasks such as making an expensive connection to a database, defer those tasks to occur after startup.
If possible, cache data locally rather than making expensive network calls during the FolderSwitch and BeforeFolderSwitch events of an explorer, or Open events of an item.
Be aware that all calls to the Outlook object model execute on Outlook's main foreground thread. Avoid making long-running Outlook object model calls if possible.
In Outlook 2013, calls to the Outlook object model return E_RPC_WRONG_THREAD when the Outlook object model is called from a background thread.
Polling is an expensive operation, so always prefer an event-driven model over polling.
System administrator control over add-ins
The user has control over which add-ins run on their computer. Beginning with Office 2013, system administrators can configure an enhanced level of control for add-ins by using group policy. Group policy will always override user settings and users are prevented from changing add-in settings for add-ins that have been configured by the group policy List of Managed Add-ins.
For Outlook, the registry keys and settings are described in the following tables.
|Description||This policy setting allows you to specify the list of managed add-ins are always enabled, always disabled (blocked), or configurable by the user.
NOTE: Here, the term "managed" refers to add-ins that are handled by the group policy, and does not relate to add-ins being developed in managed programming languages.
|String||ProgID of the add-in|
|Values||Specify the value as follows:
0 = always disabled (blocked)
1 = always enabled
2 = configurable by the user and not blocked by the Block all unmanaged add-ins policy setting when enabled.
Use the Registry Editor on the client computer where the add-in is installed, in order to obtain the ProgID for an add-in: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins or HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\Outlook\Addins
If you disable or do not enable this policy setting, the list of managed add-ins will be deleted. If the Block all unmanaged add-ins policy setting is enabled, then all add-ins are blocked.
Add-ins that are disabled by this policy will never be disabled by the Outlook add-in disabling feature, which disables add-ins for performance, resiliency, or reliability reasons.
If the user chooses "Always enable this add-in", the registry is updated to include details about the add-in that is to be exempted from the automatic disabling feature.
|String||ProgID of the add-in|
|Values||Hex value between 1 and A indicating the reason the add-in was originally disabled:
0x00000001 Boot load (LoadBehavior = 3)
0x00000002 Demand load (LoadBehavior = 9)
0x00000004 Handling FolderSwitch event
0x00000005 Handling BeforeFolderSwitch event
0x00000006 Item Open
0x00000007 Iteration Count
0x00000009 Crash, but not disabled because add-in is in the allow list
0x0000000A Crash, but not disabled because user selected no in disable dialog
NOTE: The x.0 placeholder represents the version of Office (16.0 = Office 2016, 15.0 = Office 2013).
If you re-enable an add-in that caused a performance problem at one time, users may experience performance problems in the future in the Office program for which the add-in is loaded.
To block add-ins that are not managed by this policy setting, you must also configure the Block all unmanaged add-ins policy setting.
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