If you are migrating from the classic version of Outlook to the new Outlook for Windows, you may notice that some of your familiar add-ins no longer appear or work. This happens because the new Outlook is built on a web-based platform that only supports web add-ins, not COM or VSTO-based add-ins used by the classic client. This article explains why this change occurs and provides a clear path to identify unsupported add-ins and replace them with supported web add-ins. You will learn how to check which add-ins are compatible and where to find alternatives in the Microsoft AppSource store.
Key Takeaways: Replacing Classic Outlook Add-ins with Web Add-ins
- File > Options > Add-ins in classic Outlook: Lists all installed COM and VSTO add-ins that will not work in new Outlook.
- Get Add-ins button on the Home ribbon in new Outlook: Opens the AppSource store where you can find web-based alternatives.
- Admin-managed add-ins in the Microsoft 365 admin center: Allows IT admins to deploy web add-ins to users who have switched to new Outlook.
Why Classic Outlook Add-ins Stop Working in New Outlook
Classic Outlook for Windows supports multiple add-in architectures: COM add-ins built with C++ or .NET, VSTO add-ins using Visual Studio Tools for Office, and web add-ins using HTML, CSS, and JavaScript. The new Outlook for Windows is a progressive web app that runs inside a browser-like container. This architecture cannot load COM or VSTO components because those technologies require direct access to the Windows registry and local system resources. Only web add-ins, which run in a sandboxed browser environment, are supported. When you switch to new Outlook, any COM or VSTO add-in is ignored by the application. The add-in entry disappears from the ribbon and the settings page. This is not a bug but a deliberate design decision to improve security, performance, and cross-platform consistency.
How to Identify Unsupported Add-ins
Before migrating, review your current add-in list in classic Outlook. Open classic Outlook and go to File > Options > Add-ins. The list shows all installed add-ins with their type under the Type column. COM and VSTO add-ins are labeled as COM Add-in or VSTO Add-in. Web add-ins are labeled as App for Outlook. Write down the names of all COM and VSTO add-ins. These are the ones you need to replace.
Steps to Find and Install Web Add-ins in New Outlook
Once you have identified the unsupported add-ins, follow these steps to find web-based replacements and install them in the new Outlook.
- Open new Outlook for Windows
Launch the new Outlook app. If you are still in classic Outlook, toggle the Try the new Outlook switch in the top-right corner of the window. Wait for the interface to reload. - Go to Get Add-ins
On the Home ribbon, click the Get Add-ins button. Alternatively, click the ellipsis (three dots) on the left navigation bar and select Get Add-ins. This opens the AppSource store inside Outlook. - Search for a replacement add-in
In the search bar at the top of the Add-ins window, type the name of the add-in you need to replace. For example, if you used a PDF tool, search for PDF. AppSource returns only web add-ins that are compatible with new Outlook. Browse the results and read the description to confirm it offers the same functionality. - Install the web add-in
Click the add-in card to open its details page. Click the Add button. A confirmation dialog may appear asking for permissions. Review the permissions and click Continue. The add-in is added to your Outlook ribbon and can be accessed from the Home tab or the ellipsis menu depending on the add-in design. - Test the add-in
Open an email or calendar item and locate the add-in in the ribbon. Click it to verify it loads correctly. If the add-in does not appear, go to Settings > General > Manage Add-ins and ensure the toggle for that add-in is turned on.
If Your Add-in Has No Direct Web Replacement
Not every classic add-in has an identical web version. If you cannot find a match in AppSource, consider these alternatives.
Contact the Vendor
Visit the vendor website for the classic add-in you used. Many software vendors have already released web versions of their add-ins. Look for a download link labeled Outlook on the web, Outlook Web App, or new Outlook. If the vendor offers only a COM add-in, ask their support team about a web add-in roadmap.
Use Built-in Outlook Features
Some classic add-ins replicate functionality that already exists in new Outlook. For example, a signature management add-in may be replaced by the built-in Signature feature under Settings > Mail > Compose and Reply. A PDF attachment add-in may be replaced by the built-in PDF viewer in Outlook. Check the new Outlook settings before searching for a third-party alternative.
Ask Your IT Administrator to Deploy Web Add-ins
If you are in an organization, your IT admin can deploy web add-ins to all users through the Microsoft 365 admin center. Admins go to Settings > Integrated apps > Get apps and select a web add-in from AppSource. They can pin the add-in to the ribbon for all users. This method ensures that everyone in the organization has access to the same web add-in without individual installation steps.
Common Issues When Switching to Web Add-ins
Add-in Does Not Appear in Ribbon After Installation
If a web add-in is installed but does not show up in the ribbon, click the ellipsis menu on the ribbon and check if the add-in is listed under Apps. If it is there, right-click it and select Add to Ribbon. If the add-in still does not appear, go to Settings > General > Manage Add-ins and verify the toggle is enabled. Some add-ins only appear when you are viewing a specific item type, such as an email or a meeting request.
Add-in Requests Permissions That Seem Excessive
Web add-ins request permissions such as read and write access to mail items or calendar. Review the permissions on the AppSource details page before installing. If an add-in asks for permissions that do not match its function, do not install it. Report suspicious add-ins to Microsoft by clicking Report abuse on the AppSource page.
Add-in Slows Down Outlook Performance
Web add-ins run in a browser process. If an add-in uses excessive CPU or memory, it can slow down Outlook. Open Task Manager by pressing Ctrl+Shift+Escape and check the Outlook processes. If a specific add-in is using high resources, disable it by going to Settings > General > Manage Add-ins and toggling it off. Look for a lighter alternative in AppSource.
| Item | Classic Outlook (COM/VSTO) | New Outlook (Web) |
|---|---|---|
| Add-in architecture | COM or VSTO components that access local system resources | HTML, CSS, and JavaScript running in a sandboxed browser container |
| Installation method | MSI installer, setup.exe, or registry-based deployment | AppSource store or admin deployment via integrated apps |
| Supported Outlook versions | Classic Outlook for Windows only | New Outlook for Windows, Outlook on the web, Outlook for Mac |
| Security model | Full trust; can access file system, registry, and network | Permission-based; requires explicit user consent for each scope |
| Update process | Manual download or automatic update from vendor | Automatic updates from AppSource; no user action needed |
| IT admin control | Group Policy, registry keys, or SCCM deployment | Microsoft 365 admin center > Integrated apps |
Now that you understand the difference between classic and web add-ins, you can confidently migrate to the new Outlook. Start by checking your classic add-in list and searching AppSource for web replacements. If a direct replacement is not available, contact the vendor or use built-in Outlook features. As a final tip, pin your most-used web add-in to the ribbon by right-clicking it in the Apps menu and selecting Add to Ribbon for faster access.