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How to fix add-in initialization issues

Troubleshoot issues where the SecureMailMerge add-in is stuck loading, fails to initialize, or shows a blank panel.

Contents

Symptoms

  • The add-in panel opens but stays blank or shows a loading spinner indefinitely
  • You see a “Loading…” or “Initializing…” message that never completes
  • The add-in panel is completely white or empty
  • The add-in briefly loads then disappears

Common Causes

  • Browser cache or Outlook web cache is corrupted
  • Network connectivity issues blocking the add-in from loading
  • Browser storage (cookies/IndexedDB) is blocked by privacy settings
  • An outdated version of the add-in is cached
  • Corporate proxy or firewall blocking add-in resources

Step-by-Step Fixes

1. Hard refresh the add-in

Close and reopen the email compose window. If using Outlook on the Web, try a hard refresh of the browser page (Ctrl + Shift + R or Cmd + Shift + R on Mac).

2. Clear the Outlook add-in cache

For Outlook Desktop (Windows):

  1. Close Outlook completely
  2. Press Win + R, type %LOCALAPPDATA%\Microsoft\Outlook and press Enter
  3. Delete the contents of the WebExtCache or Wef folder if present
  4. Restart Outlook

For Outlook on the Web:

  1. Clear your browser cache and cookies for outlook.office.com and outlook.office365.com
  2. Alternatively, try opening Outlook in a private/incognito browser window

3. Check that browser storage is not blocked

If your browser blocks third-party cookies or storage access, the add-in cannot start. See our dedicated guide: Access to browser storage is blocked.

4. Check your network connection

The add-in needs to load resources from the internet. Verify that:

  • Your internet connection is working
  • No VPN or proxy is blocking *.securemailmerge.com
  • Your corporate firewall allows connections to our servers (see IT Security for required domains)

5. Remove and reinstall the add-in

  1. In Outlook, go to the Apps menu (or Get Add-ins)
  2. Find SecureMailMerge and click Remove
  3. Close and reopen Outlook
  4. Reinstall from the Apps menu or the Microsoft AppSource listing

6. Try a different browser or Outlook client

If you are using Outlook on the Web, try a different browser (Chrome, Edge, Firefox). If you are on Outlook Desktop, try Outlook on the Web at outlook.office.com to isolate whether the issue is specific to your Outlook installation.