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Editorial Team
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Asked: 2026-05-22T11:30:40+00:00

I have an add-in for Outlook 2010, created with Visual Studio 2010 and using

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I have an add-in for Outlook 2010, created with Visual Studio 2010 and using VSTO. The projects target framework is .NET framework 4 Client Profile (as default).

Is there any way to change the target framework to .NET framework 3.5 or .NET framework 3.5 profile for my project? The project itself doesn’t allow me to make the change and reverts back to .NET 4, when using the project Properties -> Application tab.

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I am aware that I may need to make changes to my code, in order for it compile for .NET Framework 3.5.

Best regards

MLJ

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1 Answer

  1. Editorial Team

    Because a new VSTO project references the correct versions of the Office.Tools assemblies for that .net framework I don’t recommend changing the target framework version like that.

    In the past I have simply created a new project, then added all my code to the new add-in. This ensures you have the correct versions of the VSTO Tools referenced, and the correct setup for that version of the .net framework.

    At a minimum create a new project, then edit your old .csproj file, copy the Office.Tools.* references from the new .csproj file into your old one, and try to manually modify the old .csproj file to match the new one. Multi-targeting is not as nice a story with VSTO as other project types 🙂

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