Many business users rely on COM add-ins to extend Outlook with custom email processing, CRM integrations, or compliance tools. The new Outlook for Windows, currently in preview, does not support COM add-ins because it is built on a web-based Outlook platform. This article explains why COM add-ins are not available in new Outlook, what Microsoft plans for add-in compatibility, and how to switch back to classic Outlook to keep your existing add-ins working.
Key Takeaways: COM Add-in Support in New Outlook
- Toggle “Try the new Outlook” off: Returns you to classic Outlook where all COM add-ins remain active and functional.
- Web add-ins only in new Outlook: New Outlook supports Exchange Web Services and Office Add-ins framework, not COM components.
- Microsoft’s roadmap for add-in migration: Microsoft plans to extend the web add-in framework but has not announced a COM compatibility layer.
Why New Outlook Does Not Support COM Add-ins
Classic Outlook (part of Microsoft 365 desktop apps) loads COM add-ins as in-process DLLs that run inside the Outlook.exe process. These add-ins have deep access to the Outlook object model, including message events, folder operations, and custom forms. New Outlook is a progressive web app (PWA) that runs in a sandboxed WebView2 environment. The PWA architecture does not allow native DLL loading for security and stability reasons.
Microsoft designed new Outlook to be faster, more secure, and easier to update across platforms. COM add-ins introduce instability — a poorly coded add-in can crash the entire Outlook process. In new Outlook, only web add-ins built with the Office Add-ins manifest (XML-based) and JavaScript can run. These web add-ins communicate through a REST API layer and do not have direct access to the Windows registry or file system.
What Happens When You Enable New Outlook with COM Add-ins Installed
If you toggle on “Try the new Outlook” while COM add-ins are installed in classic Outlook, the new Outlook ignores those add-ins entirely. You will not see them in the ribbon or in the Add-ins dialog. The COM add-ins remain installed in the classic Outlook profile but are simply not loaded. When you switch back to classic Outlook, the add-ins reappear with their previous settings intact.
How to Switch Back to Classic Outlook to Keep COM Add-ins Working
If you need your COM add-ins today, the only reliable workaround is to disable new Outlook and return to classic Outlook. Follow these steps.
- Open the new Outlook toggle
In the upper-right corner of the Outlook window, locate the toggle switch labeled “Try the new Outlook.” If the toggle is blue and set to On, click it once. - Confirm the switch to classic Outlook
A dialog appears asking “Turn off new Outlook?” Click the “Turn off” button. Outlook closes and reopens in classic mode. - Verify your COM add-ins are loaded
In classic Outlook, go to File > Options > Add-ins. Under “Manage,” select “COM Add-ins” from the dropdown and click “Go.” Confirm that your add-ins are checked and listed as Active. - Prevent the new Outlook prompt from reappearing
In classic Outlook, go to File > Options > General. Under “Outlook start and exit options,” uncheck “Enable the new Outlook experience.” This stops the toggle from being displayed again.
What Microsoft Plans for Add-in Compatibility in New Outlook
Microsoft has not announced a COM compatibility layer for new Outlook. The company is investing in the Office Add-ins platform (web add-ins) as the future extensibility model. Some features that COM add-ins provide — such as custom message classification, email archiving rules, and third-party security tools — are being rebuilt as web add-ins by their vendors. For example, Microsoft itself has released a web-based version of the Microsoft 365 Compliance add-in for new Outlook.
If you rely on a specific COM add-in, check with the vendor for a web add-in version. Vendors like Evernote, Zoom, and DocuSign already offer web add-ins that work in new Outlook. For custom in-house COM add-ins, you must either rewrite them as web add-ins or continue using classic Outlook.
If You Must Stay on New Outlook: Alternative Approaches
“Can I run both classic and new Outlook side by side?”
No. Windows only allows one Outlook process per profile at a time. If you have multiple Microsoft 365 accounts, you can sign in to one account in classic Outlook and another account in new Outlook, but COM add-ins from the classic instance will not affect the new Outlook instance.
“What about VBA macros — do they still work?”
VBA macros are not supported in new Outlook either. Macros run inside the classic Outlook process and rely on the same COM object model. If you use VBA macros for automation, you must stay on classic Outlook.
“Are there third-party tools that bridge COM add-ins to new Outlook?”
As of 2025, no reliable third-party bridge exists. Some tools claim to convert COM add-ins to web add-ins, but they are experimental and rarely work with enterprise-grade add-ins. The safest path is to wait for the vendor to release an official web add-in.
Classic Outlook vs New Outlook: Add-in Support Comparison
| Item | Classic Outlook | New Outlook |
|---|---|---|
| COM add-in loading | Full support via in-process DLL | Not supported |
| Web add-in (Office Add-ins) | Supported | Supported |
| VBA macros | Supported | Not supported |
| Custom forms | Supported | Not supported |
| Third-party CRM integration | Works via COM add-in | Requires web add-in |
New Outlook currently lacks support for COM add-ins, VBA macros, and custom forms. Classic Outlook remains the only option for users who depend on these features.
You can keep using classic Outlook as long as your organization does not force the switch to new Outlook. Monitor the Microsoft 365 Message Center for announcements about web add-in improvements. If you must modernize, ask your add-in vendor for a timeline on web add-in support. For now, the toggle switch in the upper-right corner is your quickest workaround to restore all COM add-in functionality.