This issue usually occurs when:
A new ExtendSync version is available but cached files are blocking the update, or
The app loads but won’t refresh to the latest version due to stale cache.
Because Microsoft add-ins run on HTML and JavaScript across multiple environments, caching issues can occasionally prevent updates from loading correctly. Outlook caches add-ins for speed, but when the cache doesn’t refresh properly after an update, you may see:
A spinning icon,
Three dots, or
A blank white screen inside the ExtendSync panel.
Why does this happen and how can I fix it?
Microsoft add-ins are web-based (HTML + JavaScript), and performance relies on browser caching.
Add-ins often remain cached even after a new version is released.
If multiple add-ins are installed, the auto-cache refresh process may fail.
Clearing or reloading the cache forces Outlook to pull the latest version of ExtendSync.
Follow the steps below to fully clear your add-in cache and get ExtendSync working again.
Start with the first section and move to the next if the issue persists.
Windows and Mac users, try this first
Step 1: Reload the add-in
Right-click anywhere inside the ExtendSync pane → Reload/Refresh.
If you don’t see “Reload”: click inside the pane and press F5.
Step 2: Fully restart Outlook
Fully close and restart Outlook.
Open ExtendSync again and test if it loads normally.
If the problem persists, continue with OS-specific steps below.
Microsoft Windows Users
🚨 Important note about cache engines
Microsoft does not use your default browser, it uses Edge or IE to render add-ins such as CloudExtend.
Follow the instructions in this article to determine the browser used by Microsoft for your add-in and then clear that cache.
If you're not sure you can clear the cache in Edge and IE.
Step 1: Clear the Office Add-In Cache
Close Outlook completely.
In File Explorer, paste and open:
%LOCALAPPDATA%\Microsoft\Office\16.0\Wef\Back up (optional) then delete everything inside this folder.
If the path exists, also clear this folder:
%userprofile%\AppData\Local\Packages\Microsoft.Win32WebViewHost_cw5n1h2txyewy\AC\#!123\INetCache\Reopen Outlook and launch ExtendSync.
Step 2: Hard-Reload the Add-In Storage
Open the ExtendSync panel in Outlook.
Right-click inside the add-in → Inspect (opens DevTools).
Go to Application → Local Storage → right-click your ExtendSync origin → Clear.
Do the same for Session Storage.
Press Ctrl + R (DevTools focus) or F5 (pane focus) to reload.
Mac Users
If you're working on a Mac and the first step above did not work then continue with the steps below.
Option 1: Clear Cached Web Content
Click the ⓘ (info) icon at top-right of the add-in → Clear Web Cache.
Option 2: Clear Safari Cache
Exit Outlook.
Clear Safari cache by following the instructions here.
Reopen Outlook → open ExtendSync.
If the problem persists, manually clear the Office cache below.
Still not working?
If clearing browser cache did not resolve the issue then delete your Office cache following one of the methods below.
Manually clear Office add-in cache
Manual Method
Exit Outlook
Manually delete the contents of the folders below (folders may vary by OS/Outlook build):
~/Library/Containers/com.Microsoft.OsfWebHost/Data/
(Optional. )If that folder doesn't exist, check for the following folders. If found, delete the contents of the folder/s:
/Library/Containers/com.microsoft.outlook/Data/Library/Caches/http://com.microsoft.Office365ServiceV2/Data/Caches/com.microsoft.Office365ServiceV2/Open Outlook and load CloudExtend again.
💡 Note, the existence of the folders below is dependent on the combination of your Outlook version number and your OS version.
Script Method
If you have trouble locating all the files above just prefer a faster option you can download this script as a zip file.
Expand the zip file, right-click on Clear-Cache.app, and choose open.
You won't get a confirmation but your office cache files should now be cleared.
Clear WebKit cache for Outlook
If manually clearing the Office cache on your Mac did not resolve your issue then this should do the trick:
Exit Outlook.
Run this command from Terminal (replace
YOURNAMEwith your Mac username)
rm -r /Users/YOURNAME/Library/Containers/com.Microsoft.Outlook/Data/Library/Caches/WebKit/If the rm command is not found your path variable may have been set.
Check with your admin before running the command below as this will reset your path.
export PATH=/sbin:/bin:/usr/sbin:/usr/bin
Open Outlook and load CloudExtend again
Why this works
Outlook caches add-in assets in Office/Outlook add-in cache folders (WebView2/IE on Windows, WebKit on macOS). After an ExtendSync update, old files can prevent the new bundle from loading. Clearing these folders forces Outlook to fetch the latest version.
Still stuck?
Try removing and re-adding the add-in (File → Manage Add-ins / Get Add-ins → My Add-ins).
Confirm you’re on a current Microsoft 365 build.
Contact us with details (OS, Outlook version, steps tried, screenshots):
💬 In-app chat (bottom-right of our Help Center)