You want to compare New Outlook with Classic Outlook without fully switching. Running both versions side by side on the same computer lets you test features while keeping your old setup intact. Microsoft added this option in late 2023 for Windows 11 and Windows 10 users who have a Microsoft 365 subscription or a supported work or school account. This article explains where to find the toggle, how to enable side-by-side mode, and what each version can and cannot do.
Key Takeaways: Running Both Outlook Versions Together
- Toggle in Classic Outlook > File > Options > General: Enables the “Try the new Outlook” switch that launches New Outlook while Classic Outlook remains open
- Separate desktop shortcuts: New Outlook installs as a separate app from the Microsoft Store; Classic Outlook stays as part of Office
- Profile and data separation: Each version uses its own cache and settings, so changes in one do not affect the other
How the Side-by-Side Feature Works
The side-by-side option lets you open New Outlook and Classic Outlook at the same time on the same Windows desktop. This is not a split window inside one program. Instead, you get two separate Outlook windows that can be arranged side by side using standard Windows snapping or manual resizing.
Classic Outlook is the traditional Win32 desktop application installed with Microsoft 365 or Office 2019/2021. New Outlook is a modern Universal Windows Platform app distributed through the Microsoft Store. When you turn on the side-by-side toggle, Classic Outlook stays open and New Outlook launches as a second window. Both versions connect to the same mailbox, but they use independent caches and settings. This means you can test New Outlook features such as the new calendar layout, integrated To Do, or the unified inbox without risking your Classic Outlook configuration.
Prerequisites for Side-by-Side Mode
Your account must be one of the following types: a Microsoft 365 personal or family subscription, a Microsoft 365 Business Basic, Standard, or Premium account, or an Exchange Online mailbox through a work or school. Free Outlook.com accounts also qualify. Windows 11 users get the toggle automatically after the October 2023 update. Windows 10 users need the latest Windows 10 version 22H2 with cumulative update KB5031445 or later. Classic Outlook version must be 2023 build 16.0.16924.20000 or newer.
Where to Find the Side-by-Side Toggle
The toggle is located inside Classic Outlook. Follow these steps to enable it:
- Open Classic Outlook
Launch Outlook from your Start menu or desktop shortcut. Make sure you are signed into your Microsoft 365 or Exchange account. - Go to File > Options
Click the File tab in the top-left corner, then click Options at the bottom of the left pane. - Select the General tab
In the Outlook Options dialog, click General on the left side. - Turn on the New Outlook toggle
Under the “Outlook for Windows” section, you will see a checkbox labeled “Try the new Outlook.” Check this box. A confirmation dialog appears asking if you want to switch. Click Yes. - Close and reopen Classic Outlook
Close Classic Outlook. When you reopen it, the New Outlook app starts automatically. Both windows appear on your desktop. Classic Outlook remains open in the background and can be brought forward from the taskbar.
If you do not see the toggle, your account type or Outlook version may not support it. Check that you have installed all pending Windows and Office updates.
How to Arrange the Two Windows Side by Side
After both versions are open, you can snap them to opposite sides of the screen. Click the title bar of one window and drag it to the left edge of your monitor until a transparent outline appears. Release the mouse. Then click the title bar of the other window and drag it to the right edge. Each window occupies half the screen. You can also use the keyboard shortcut Windows key + Left Arrow for the left window and Windows key + Right Arrow for the right window. Adjust the divider to give more space to the version you are testing.
Common Limitations and Things to Avoid
New Outlook Crashes or Does Not Load
If New Outlook fails to start, close Classic Outlook and restart both. Open Classic Outlook first, then check the toggle again. If the problem persists, uninstall New Outlook from Settings > Apps > Installed apps, then reinstall it from the Microsoft Store. Your data is not affected because New Outlook stores its cache separately.
Classic Outlook Closes When You Open New Outlook
This happens when the side-by-side toggle is off. Go to File > Options > General and ensure the checkbox is checked. If Classic Outlook still closes, your account may be configured to force the switch. In that case, contact your IT administrator to disable the policy that blocks side-by-side mode.
Shared Mailboxes or Public Folders Do Not Appear in New Outlook
New Outlook does not support all Classic Outlook features. Shared mailboxes added through Advanced account settings in Classic Outlook do not carry over. You must add them again inside New Outlook by going to Settings > Accounts > Email accounts > Add account. Public folders are not available in New Outlook at all. Use Classic Outlook for those tasks.
Changes Made in One Version Affect the Server
While each version uses its own local cache, actions that modify server data such as deleting an email, moving a message to a folder, or creating a calendar event are sent to the server immediately. Both versions see the change after a short sync. If you delete an email in New Outlook, it disappears from Classic Outlook as well. Always test with non-critical items first.
New Outlook vs Classic Outlook: Key Differences When Running Side by Side
| Item | New Outlook | Classic Outlook |
|---|---|---|
| Installation method | Microsoft Store app | Office desktop installer (MSI or Click-to-Run) |
| Account types supported | Microsoft 365, Exchange Online, Outlook.com, Google, Yahoo, iCloud | Microsoft 365, Exchange on-premises, POP3, IMAP, Outlook.com |
| Offline access | Limited to cached mode with no offline data file (.ost) | Full offline access with .ost file and offline address book |
| COM add-ins and macros | Not supported | Full support for VBA macros, COM add-ins, and third-party integrations |
| Public folders | Not available | Fully supported |
| Search index | Uses Windows Search with a separate index | Uses Windows Search with its own index or built-in search |
| Calendar sharing | Internet calendar subscriptions and Microsoft 365 sharing only | Full sharing with delegate access, internet calendars, and free/busy publishing |
Running both versions side by side gives you a safe way to evaluate New Outlook before committing to a switch. You can move your daily work gradually by testing features such as the new mail composition interface or the integrated Microsoft To Do while keeping Classic Outlook for tasks that require add-ins or public folders. To disable side-by-side mode, uncheck the toggle in Classic Outlook and restart. New Outlook will no longer start, and Classic Outlook returns to its normal behavior.