On some clients the Sendent Outlook plugin keeps disabling on start-up. This might be due alleged performance issues at the very start-up of Microsoft Outlook or a crash that might have happened in the past of Outlook itself.
In Outlook there's a mechanism in place that puts Outlook add-ins on a list. This list causes the behavior that add-in is disabling at the very start of Outlook.
As a administrator you can solve this behavior by modifying a registry entry.
Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\SendentOutlook
There we look for the REG_DWORD:
LoadBehavior
In case the add-in keeps disabling at start-up this value is likely not '3'.
If you're a administrator, please make sure to close Microsoft Outlook (process also not running in the background!). From there you can overwrite the LoadBehavior value and set it to '3'. If you start Outlook now, the add-in should launch like it normally would.
This registry entry can also be pushed as a GPO to all your users where the Outlook add-in is installed.
Reference chart:
| Value (in decimal) | VSTO Add-in status | VSTO Add-in load behavior | Description |
|---|---|---|---|
| 0 | Unloaded | Don't load automatically | The application never tries to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. If the VSTO Add-in is successfully loaded, the LoadBehavior value remains 0, but the status of the VSTO Add-in in the COM Add-ins dialog box is updated to indicate that the VSTO Add-in is loaded. |
| 1 | Loaded | Don't load automatically | The application never tries to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. Although the COM Add-ins dialog box indicates that the VSTO Add-in is loaded after the application starts, the VSTO Add-in isn't loaded until it's loaded manually or programmatically. If the application successfully loads the VSTO Add-in, the LoadBehavior value changes to 0, and remains at 0 after the application closes. |
| 2 | Unloaded | Load at startup | The application doesn't try to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. If the application successfully loads the VSTO Add-in, the LoadBehavior value changes to 3, and remains at 3 after the application closes. |
| 3 | Loaded | Load at startup | The application tries to load the VSTO Add-in when the application starts. This is the default value when you build or publish a VSTO Add-in in Visual Studio. If the application successfully loads the VSTO Add-in, the LoadBehavior value remains 3. If an error occurs when loading the VSTO Add-in, the LoadBehavior value changes to 2, and remains at 2 after the application closes. |
| 8 | Unloaded | Load on demand | The application doesn't try to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. If the application successfully loads the VSTO Add-in, the LoadBehavior value changes to 9. |
| 9 | Loaded | Load on demand | The VSTO Add-in will be loaded only when the application requires it. Such as when a user selects a UI element that uses functionality in the VSTO Add-in (for example, a custom button in the Ribbon). If the application successfully loads the VSTO Add-in, the LoadBehavior value remains 9, but the status of the VSTO Add-in in the COM Add-ins dialog box is updated to indicate that the VSTO Add-in is currently loaded. If an error occurs when loading the VSTO Add-in, the LoadBehavior value changes to 8. |
| 16 | Loaded | Load first time, then load on demand | Set this value if you want your VSTO Add-in to be loaded on demand. The application loads the VSTO Add-in when the user runs the application for the first time. The next time the user runs the application, the application loads any UI elements that are defined by the VSTO Add-in. However, the VSTO Add-in isn't loaded until the user selects a UI element that is associated with the VSTO Add-in. When the application successfully loads the VSTO Add-in for the first time, the LoadBehavior value remains 16 while the VSTO Add-in is loaded. After the application closes, the LoadBehavior value changes to 9. |
Source: https://learn.microsoft.com/en-us/visualstudio/vsto/registry-entries-for-vsto-add-ins?view=vs-2022