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Troubleshooting: Microsoft Outlook Memory Leak (solved)
Troubleshooting: Microsoft Outlook Memory Leak (solved)

OLNS | Learn more about a known Microsoft issue that causes memory leaks with add-ins

Updated over a week ago


Memory leaks happen when opening and closing emails in new windows (by double-clicking) with pinnable add-in with Edge Webview. The memory usage of Desktop App Web Viewer process grows to an extent that it might freeze Outlook or reaches the add-in memory limit and crashes ultimately, rendering add-ins unusable.


  • Microsoft has provided a fix for this issue with the August 2020 Microsoft update for Windows users of 1903 and 1909 (see this article from Microsoft for details).

  • For users in 2004 it was addressed with the September 8, 2020 update (see this article from Microsoft for details, note that this update includes everything in the September 3 preview update that specifically cites addressing the issue with pinned apps.


Although Microsoft has acknowledged they have fixed the issue we are keeping the detail below for historical context.

📌 This was a known Microsoft issue tracked by them on GitHub:

Affected users

Users with Microsoft add-ins such as CloudExtend running in Edge Webview. Beginning with Office 365 version 16.0.11629 and Windows 10 version 1903, Office Add-ins running on Office 365 for Windows will use a Microsoft Edge WebView as the runtime. The selection of Edge WebView is entirely decided by Microsoft.

How to reproduce

Step 1: Open Outlook desktop app and log in.

Step 2: Open an email, and open a pinnable add-in (CloudExtend Outlook for NetSuite in this case).

Step 3: Pin the task pane.

Step 4: Open Task Manager.

Step 5: Double click an email in the inbox, wait for it to open in a new window, and wait for the pinnable add-in to load.

Step 6: Close the new window.

Step 7: Repeat Steps 4 and 5 multiple times.

Step 8: The memory usage of Desktop App Web Viewer keeps growing at a significant rate.

Suggested Workarounds

Microsoft recommends users install the August 2020 update (see here).

If you are unable to install the update then choose one of the below two options

  • If keeping the task pane pinned is important to you then periodically open Task Manager (Ctrl-Shift-Esc), find Desktop App Web Viewer processes
    Right-click → End task (Temporary workaround when freezing happens).

  • Do not pin the add-in (suggested by Microsoft).

How to End task the Desktop App Web Viewer

How to 'end task' the Desktop App Web Viewer'

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