Users are complaining that the new Windows version of Outlook is running slowly.

Windows 11 offers two versions of Outlook: Outlook Classic, a Win32 desktop application, and 'New Outlook.' It has been reported that this New Outlook is extremely slow in certain operations.

Microsoft's new Outlook takes 10 seconds to do what Outlook Classic does instantly on Windows
https://www.windowslatest.com/2026/06/15/microsofts-new-outlook-takes-10-seconds-to-do-what-outlook-classic-does-instantly-on-windows/

One user reported that 'opening emails from Windows notifications is slow in the new Outlook.'

The following describes how Outlook Classic behaves when opening an email from a notification.


The following describes how it works in the new Outlook: It takes nearly 10 seconds from when Outlook starts up until the email body is displayed.


This user added, 'For some reason, it's faster to see the notification and open Outlook directly from the Start menu.'


The new Outlook is built on WebView2, which essentially functions as a browser window loading Outlook.com. The app has to initialize or restart the web layer, perform authentication, load the relevant email threads, and render all of that via the web engine.

Due to these factors, the new Outlook consumes more memory. The new Outlook runs as 10 separate processes in Task Manager, including WebView2 Manager, multiple WebView2 Utility processes, WebView2 GPU Process, and WebView2 Service Worker, each consuming memory independently. Outlook Classic, on the other hand, operates as a single, compact process.

Microsoft had previously been aware of the offline functionality and performance limitations of the new Outlook, and had been testing a new API called 'Delayed Message Timing' to help diagnose performance issues in WebView2 apps. However, they were unable to confirm that the API was being used when this user clicked on an Outlook notification.

The user stated, 'Outlook Classic processes emails natively by caching them locally, while the web app, by design, always communicates with the server. At this point, if you consider the speed of notification processing to be important for your business, Outlook Classic is the more reliable choice.'