You have switched to the new Outlook for Windows but still need to access your classic Outlook profile for specific tasks or data. The side-by-side mode lets you run both versions at the same time, but the option to enable it is hidden after you leave classic Outlook. This article explains where to find the side-by-side toggle in the new Outlook and how to turn it on.
Key Takeaways: Enable Side-by-Side Mode in New Outlook
- New Outlook > Settings > General > Try the new Outlook: Toggle to switch between classic and new Outlook; no side-by-side option here.
- Registry key HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\General: Add DWORD value “SideBySide” set to 1 to re-enable the side-by-side toggle.
- Classic Outlook > Help > Try the new Outlook: Turn off the toggle to return to classic Outlook and regain access to the side-by-side switch.
How Side-by-Side Mode Works and Why It Disappears
Side-by-side mode allows you to run classic Outlook and new Outlook simultaneously on the same Windows machine. When you enable this mode, a toggle appears in the title bar of classic Outlook labeled “Try the new Outlook.” Clicking that toggle switches between the two versions, but the option to keep both running at once is controlled by a separate setting.
In classic Outlook, the side-by-side toggle is visible under File > Options > General. The checkbox reads “Enable side-by-side mode” and is available only when the new Outlook is installed. Once you switch fully to new Outlook and close classic Outlook, the side-by-side option disappears from the new Outlook interface. This happens because Microsoft designed the side-by-side feature as a transitional tool for classic Outlook users, not as a permanent setting within new Outlook.
Prerequisites for Side-by-Side Mode
Before you can run both versions, confirm these requirements:
- Windows 10 version 1903 or later, or Windows 11
- Microsoft 365 subscription with the new Outlook toggle available
- Classic Outlook installed and configured with at least one email account
- New Outlook enabled via the toggle in classic Outlook
Locating the Side-by-Side Toggle After Switching to New Outlook
If you are already in new Outlook and cannot find the side-by-side option, you have two methods to re-enable it. The first method uses the new Outlook settings menu, but it only lets you switch back to classic Outlook, not run both. The second method uses a registry edit to restore the side-by-side toggle in classic Outlook.
Method 1: Use the Try the New Outlook Toggle in New Outlook
- Open New Outlook Settings
In the new Outlook window, click the gear icon in the top-right corner to open Settings. - Navigate to General
In the Settings panel, click the General tab on the left side. - Locate the Try the New Outlook Toggle
Scroll down to the section labeled “Try the new Outlook.” You will see a toggle switch. If it is on, you are in new Outlook. Turning it off switches you back to classic Outlook. - Turn Off the Toggle
Click the toggle to turn it off. Classic Outlook opens automatically. You now have access to the side-by-side option in classic Outlook. - Enable Side-by-Side in Classic Outlook
In classic Outlook, go to File > Options > General. Check the box “Enable side-by-side mode.” Click OK. The side-by-side toggle now appears in the title bar of classic Outlook.
Method 2: Use Registry Editor to Re-enable Side-by-Side Toggle
If the toggle in new Outlook does not appear or you prefer a direct method, use Registry Editor to add the side-by-side key. This method works even if you have already closed classic Outlook.
- Close All Outlook Instances
Make sure both classic and new Outlook are closed. Check Task Manager for any Outlook processes still running and end them. - Open Registry Editor
Press Windows key + R, type regedit, and press Enter. Click Yes when prompted by User Account Control. - Navigate to the Outlook General Key
In Registry Editor, go to:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\General - Create a New DWORD Value
Right-click the General folder, select New > DWORD (32-bit) Value. Name it SideBySide. - Set the Value Data
Double-click the new SideBySide entry. Set Value data to 1 and click OK. Close Registry Editor. - Open Classic Outlook
Start classic Outlook. The side-by-side toggle appears in the title bar. Click it to launch new Outlook alongside classic Outlook. Both versions now run simultaneously.
If Side-by-Side Mode Still Does Not Appear
Even after following the steps above, the side-by-side toggle may remain hidden. This section covers the most common reasons and their fixes.
The Registry Key Does Not Work
If you added the SideBySide DWORD but the toggle does not show, verify the location. The key must be under the General folder exactly as specified. A common mistake is placing the value under a different Outlook key or using a 64-bit DWORD instead of 32-bit. Delete the incorrect value and recreate it using the steps above.
New Outlook Is Not Installed
Side-by-side mode requires the new Outlook to be installed on your machine. If you uninstalled the new Outlook or never enabled the toggle, the side-by-side option is unavailable. Reinstall the new Outlook by going to classic Outlook, clicking Help > Try the new Outlook, and following the prompts. After installation, the registry method works.
Group Policy Blocks Side-by-Side Mode
In enterprise environments, an administrator may disable side-by-side mode via Group Policy. Check with your IT department. If you have local admin rights, open Local Group Policy Editor, go to User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Other, and set “Enable side-by-side mode” to Not Configured or Enabled.
Classic Outlook vs New Outlook Side-by-Side: Key Differences
| Item | Classic Outlook (Win32) | New Outlook (Mail & Calendar) |
|---|---|---|
| Installation | Part of Microsoft 365 or standalone Office | Optional toggle or Windows Mail app update |
| Interface | Full ribbon, customizable toolbar | Simplified ribbon, modern design |
| Account types | Exchange, IMAP, POP, Outlook.com, Gmail, Yahoo | Exchange, Outlook.com, Gmail, Yahoo, IMAP |
| Offline access | Full offline cache with Cached Exchange Mode | Limited offline cache, depends on account type |
| Add-in support | COM add-ins, VBA macros, third-party tools | Web add-ins only, no VBA support |
| Side-by-side toggle location | File > Options > General or title bar | Not available natively, must switch back to classic |
You can now run classic Outlook and new Outlook side by side by using the registry method or the toggle in classic Outlook. After enabling side-by-side mode, try opening a shared mailbox in classic Outlook while composing a message in new Outlook to verify both versions work independently. For advanced users, consider creating a desktop shortcut for each version to avoid confusion when both are open.