New Outlook Web Add-ins: Replace old add-ins with supported web add-ins

If you recently switched to the new Outlook for Windows or Outlook on the web, you may notice that some of your familiar add-ins no longer appear or work. Microsoft is replacing legacy COM add-ins and older XML-based add-ins with modern web add-ins that run in a sandboxed environment. This change improves security, performance, and cross-platform compatibility across Outlook, Outlook on the web, and the new Outlook for Windows. This article explains what web add-ins are, why the transition is happening, and how to find and install supported web add-ins to replace your old ones.

Why Microsoft Is Replacing Legacy Add-ins with Web Add-ins

Legacy add-ins for Outlook fall into two main categories: COM add-ins and older web-based add-ins that use the deprecated Office Add-ins platform. COM add-ins are DLL files that load directly into the Outlook process. They can cause crashes, slow startup, and security vulnerabilities because they have full access to the system. The new Outlook for Windows and Outlook on the web do not support COM add-ins at all. Older XML-based add-ins that rely on the Office 2013 add-in model also fail in the new environment.

Web add-ins use HTML, JavaScript, and CSS. They run in an isolated browser-based container. This design means a faulty add-in cannot crash Outlook or access system files. Web add-ins work identically in Outlook on the web, the new Outlook for Windows, and even in classic Outlook if you install them through the web add-in store. Microsoft is actively migrating the entire add-in ecosystem to this model. Vendors must publish a web add-in version for their product to work in the new Outlook.

What Changes for Users

If you open the new Outlook and see a message that an add-in is no longer available, or if the Add-ins ribbon button is grayed out, you are affected. Features like mail merge tools, CRM integrations, or productivity helpers that installed via a setup file or a DLL will not load. You must replace them with a web add-in from the Microsoft AppSource store or from a vendor-provided manifest URL.

Steps to Find and Install Web Add-ins in the New Outlook

The process to replace a legacy add-in with a web add-in is the same in the new Outlook for Windows and Outlook on the web. Follow these steps to locate the web version of your add-in and install it.

1. Open the Get Add-ins dialog
   In the new Outlook for Windows, click the Get Add-ins button on the Home ribbon. In Outlook on the web, click the Get Add-ins icon in the top-right corner of the reading pane or the ribbon. This opens the Microsoft AppSource store filtered for Outlook add-ins.
2. Search for your add-in by name
   Type the name of your old add-in into the search bar. For example, search for “Trello” or “DocuSign” to find the web add-in version. If the vendor has published a web add-in, it appears here. If not, look for an alternative add-in with similar features.
3. Click Add to install the web add-in
   Select the correct add-in from the search results. Review the permissions it requests. Click the Add button. The add-in installs immediately and appears in your add-in bar or ribbon.
4. Verify the add-in is working
   Open an email or calendar item where the add-in should appear. Look for the add-in icon in the reading pane or the ribbon. Click it to test that it loads correctly. If the add-in requires a login, sign in with your account credentials.
5. Remove the old legacy add-in if it still appears
   Go to File > Manage Add-ins. You see a list of all installed add-ins. Find the legacy add-in and click the three dots next to it. Select Remove. This prevents confusion and cleans up your interface.

If Your Add-In Vendor Has Not Published a Web Version

Some third-party vendors have not yet updated their products. Check the vendor website or contact support to ask about a web add-in release timeline. In the meantime, use the AppSource store to find an alternative add-in that provides the same function. For example, replace a legacy meeting scheduler with a web-based scheduling add-in like Calendly or Microsoft Bookings.

Common Issues When Replacing Legacy Add-ins with Web Add-ins

“This add-in is not supported in the new Outlook” message

This message appears directly in the add-in pane or as a banner at the top of the reading pane. The cause is that the add-in uses the old COM or XML framework. The fix is to uninstall the unsupported add-in through File > Manage Add-ins and then install the web version from AppSource. If no web version exists, you must use the classic Outlook for Windows for that specific add-in until the vendor updates it.

Web add-in does not load or shows a blank screen

A blank add-in pane often indicates that the add-in requires a login or that your browser has blocked third-party cookies. In the new Outlook for Windows, check that your system date and time are correct. In Outlook on the web, clear your browser cache and cookies for the Outlook domain. If the issue persists, remove the add-in and reinstall it from AppSource.

Add-in icon is missing from the ribbon

Some web add-ins only appear when you are reading or composing an email. Click an email in your inbox to activate the reading pane. If the add-in still does not show, go to File > Manage Add-ins, find the add-in, and ensure it is toggled on. If it is already on, remove it and add it again from AppSource.

Legacy Add-ins vs Web Add-ins: Key Differences

Item	Legacy Add-in (COM / XML)	Web Add-in (HTML / JS / CSS)
Installation method	Setup executable or registry entry	AppSource store or manifest URL
Supported in new Outlook	No	Yes
Security model	Runs in Outlook process with system access	Runs in isolated sandbox with limited permissions
Cross-platform compatibility	Windows only	Windows, Mac, web, mobile
Update mechanism	Manual update via vendor installer	Automatic update through AppSource
Performance impact	Can slow Outlook startup and cause crashes	Minimal impact; runs asynchronously

Web add-ins offer clear advantages in security, performance, and compatibility. The only downside is that some niche add-ins may not yet have a web version available. Microsoft is working with vendors to close this gap.

You can now identify which of your add-ins are legacy and replace them with supported web add-ins from AppSource. Start by reviewing your add-in list under File > Manage Add-ins. Search for each add-in in the store and install the web version. If you rely on a legacy add-in that has no web replacement, consider using the classic Outlook for Windows temporarily or finding an alternative add-in that meets your needs. For advanced users, you can deploy web add-ins centrally to your organization using the Microsoft 365 admin center under Settings > Integrated apps.