The new Outlook and COM add-ins - what stops working when you switch

Microsoft has been moving Windows users from classic Outlook (the long-running desktop app built on Win32) to the new Outlook for Windows, which is built on web technology and shares its code with Outlook on the web. New Windows installs and many Microsoft 365 users now see the new app by default, with a toggle back to classic for those who need it.

For most people the new app is fine. For anyone who relies on add-ins or automation, there is one change worth understanding before you switch.

What does not carry over

Classic Outlook supports COM add-ins and automation through its object model. That is how a generation of tools integrated with it: CRM plugins, archiving tools, PDF tools, macros, and small desktop apps that open a pre-filled email or read your calendar.

The new Outlook does not support COM add-ins or the classic object model. It supports web add-ins built on the Office Add-ins platform instead. Microsoft’s guidance on the new Outlook for Windows for administrators covers the differences, including add-in support.

In practice: if a tool you use talks to “Outlook” on your PC, check whether it means classic Outlook. If it does, it will stop working when you switch.

Things that commonly break

• VBA macros in Outlook.
• COM add-ins from vendors, especially older or niche ones.
• Desktop apps that automate Outlook: “send this file by email”, “add this to my calendar”, “reply to all attendees”.
• Some offline and PST workflows, which work differently.

Things that keep working

• Web add-ins that support the new Outlook.
• Anything that talks to Exchange or Microsoft Graph directly rather than to the Outlook app.
• Copy and paste. The unglamorous universal integration.

A real example: Jot’s meeting minutes

Jot’s meeting minutes feature (coming in the next release) has an optional “Reply all in Outlook” action that opens a reply to everyone on the meeting invite, with the minutes filled in. It talks to Outlook locally through COM: no network, no sign-in, and it only ever opens the draft for you to review, never sends. Because it uses COM, it works with classic Outlook only.

That was a deliberate trade. Doing the same through Microsoft Graph would need a sign-in and network access, which a local-first app tries to avoid. So Jot always offers Copy minutes as well, which works with any mail client, including the new Outlook. The details are in sending minutes people read.

How to plan

1. Make a list of anything that integrates with Outlook on your PC.
2. Check each vendor’s support for the new Outlook.
3. Keep classic Outlook available for now if something critical depends on it. Microsoft has said classic Outlook will continue to be supported for a period, and organisations can manage the switch.
4. Prefer integrations that use Graph or web add-ins for new tools.

The bigger picture

The move from desktop to web-based apps is happening across Microsoft 365. It brings consistency and faster updates, and it costs the deep local automation that power users relied on. If you build or buy tools, check which side of that line they sit on.

Jot is on the Microsoft Store.

Jot is a quick-capture app for Windows: one hotkey, one line, back to what you were doing. What it is, or what is still unproven.