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If by “classic or modern theme” you mean the Outlook interface, you need to switch between two separate apps: new Outlook for Windows and classic Outlook for Windows. Changing Light or Dark appearance only changes the look of the app you already have open. Here’s how to identify each version, switch between them, install classic Outlook if it’s missing, and change appearance settings.
Classic and new Outlook are different apps
Microsoft calls the redesigned app new Outlook for Windows and the traditional desktop app classic Outlook for Windows. “Modern Outlook” is a common description for the new app, not the name of a theme setting. Microsoft says new Outlook became generally available in August 2024, but access and features still vary by account, license, installation, and organization policy. Microsoft’s switching guidance explains availability.
Keep these three settings separate:
- Outlook version: Determines whether you’re using new Outlook or classic Outlook.
- App appearance: Light, Dark, or other interface options within an Outlook version.
- Message stationery: Formatting for email messages, not the Outlook window.
Windows 11’s appearance preference may affect Microsoft 365 apps when an app is set to follow the system, but changing Windows or Office theme does not turn one Outlook app into the other.
Identify which Outlook app is open
- New Outlook: Look for the Settings button near the upper-right corner. Version details are under Settings > General > About Outlook.
- Classic Outlook: Look for the File tab. Its application settings are under File > Options. In Start, it may be listed as Outlook (classic).
If you’re unsure, Microsoft’s version-identification guide shows the differences.
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Switch from classic Outlook to new Outlook
- Open classic Outlook and look for the Try the new Outlook toggle, usually near the upper-right corner.
- Turn on the toggle and allow new Outlook to download and install if prompted.
- Select Switch, then follow the sign-in or account setup prompts.
- If offered, choose Import Settings to bring supported settings into new Outlook.
Microsoft says accounts and settings can be imported during setup, but don’t assume every rule, signature, add-in, archive, profile, or workflow will transfer or behave identically. Check the items you rely on after switching. The new Outlook setup guide describes the initial process.
The toggle is not shown to everyone. Account or Office edition eligibility, an administrator’s deployment policy, or the particular Outlook installation can affect whether it appears. See Microsoft’s switching guidance if it is missing.
Switch from new Outlook back to classic Outlook
Make classic Outlook the default choice
- In new Outlook, select the upper-right toggle.
- Choose Switch back to classic Outlook.
- Submit or skip the feedback prompt, if shown.
- Open Outlook (classic) from the Windows Start menu.
Microsoft describes this as changing the default behavior so classic Outlook opens the next time you launch Outlook. The available choice depends on classic Outlook being installed. Read Microsoft’s switch-back instructions.
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Use classic Outlook just once
If you only need classic Outlook for a particular task, select the toggle and choose Use classic Outlook this time. This launches classic Outlook for that session without necessarily changing the default behavior. It can help when a workflow or add-in you need is not available in new Outlook.
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A Windows 11 PC can have new Outlook without the classic desktop app. An Outlook icon in Start does not prove that classic Outlook is installed. Search Start for Outlook (classic); if it is absent, follow Microsoft’s classic Outlook installation instructions.
- Open Microsoft’s installation page and select the required language.
- Select Download and follow the installation prompts.
- When installation finishes, launch Outlook (classic) from Start and set up or sign in to your account.
Whether you can install classic Outlook through an existing Office or Microsoft 365 entitlement depends on the edition and license. New Outlook cannot be converted into classic Outlook; they are separate applications.
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Run both Outlook apps side by side
You can keep new and classic Outlook installed and open them separately when you need to compare behavior or use a feature available in only one. Make sure you launch the intended app from Start; the Outlook and Outlook (classic) entries may be easy to confuse. Microsoft documents side-by-side use and maintains a feature comparison, updated April 14, 2026.
Choose based on the accounts and workflows you need, not on appearance alone. New Outlook suits people who prefer its simplified interface and supported connected-account workflows. Classic Outlook may be the better fit if you depend on a particular desktop feature, integration, add-in, or established workflow. Feature availability can differ, so check the comparison and test important tasks before changing how you work.
Change appearance in new Outlook
- Select Settings.
- Go to General > Appearance.
- Choose an available theme or appearance option; for dark mode, set Dark mode to Dark.
- Select Save if prompted.
The controls can vary with the app build and account. Microsoft’s dark mode instructions cover the new app as well as classic Outlook and Outlook on the web.
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Custom themes with Copilot
Eligible users may also see Themes by Copilot under Settings > General > Appearance. Select the Custom Theme tile to configure available options. This is not a universal feature: availability depends on the Outlook version, account, subscription, Copilot access, and administrator settings. See Microsoft’s Copilot theme instructions.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Change appearance in classic Outlook
To change the Office application theme, open File and look under Office Account or Options for Office Theme. Depending on the installation, you may see choices such as Colorful, Dark Gray, Black, or White. The menu location and choices can differ across Microsoft 365 and perpetual Office builds; Microsoft’s appearance guidance explains the broader controls.
For dark mode in classic Outlook, the documented route is File > Office Account > Office Theme > Black. The message reading area can have a separate background choice: you can keep the surrounding app dark while using a white message background. See Microsoft’s dark mode guide.
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Change email stationery, not the app theme
Classic Outlook’s stationery and message themes affect the formatting of HTML email, not the interface. To set stationery, use File > Options > Mail > Stationery and Fonts > Personal Stationery > Theme, choose an option, and confirm with OK. This applies to HTML-formatted messages. Microsoft’s stationery instructions explain the feature.
Troubleshoot a missing switch or app
- No “Try the new Outlook” toggle in classic: Confirm the app has a File tab and that you’re not already in new Outlook. Account or edition eligibility, an administrator policy, or the installation can affect the toggle. Ask your organization’s Microsoft 365 administrator before changing managed settings.
- No classic Outlook in Start: Search specifically for Outlook (classic). If it is not listed, check whether your Office installation includes desktop apps or install classic Outlook using Microsoft’s guidance above.
- The interface still looks new after changing colors: You changed appearance, not the app version. Use the switch-back option and ensure classic Outlook is installed.
- Only part of Outlook turns dark: The reading area or message background may have separate controls; adjust those independently.
Registry fallback: advanced and last resort
Microsoft documents a registry setting that can attempt to launch classic Outlook when the switch-back toggle is unavailable. Use this only if you understand Windows Registry editing; back up the registry first, and consider asking an administrator for help on a managed PC.
- Open Registry Editor and go to
ComputerHKEY_CURRENT_USERSoftwareMicrosoftOffice16.0OutlookPreferences. - Set the
UseNewOutlookvalue to0. - Try launching Outlook (classic) from Start.
This setting cannot install classic Outlook. It may not work if classic Outlook is absent, permissions or policy block it, the key is controlled by an organization, or the wrong shortcut is launched. Microsoft’s switch-back page describes the fallback.
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