How to fix add-in initialization issues

Learn how to fix SecureMailMerge add-in issues in Outlook, such as being stuck loading, initialization failures, blank panels, or frozen taskpanes.

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• An outdated version of the add-in is cached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.

Related

• Browser storage blocked
• App icon not showing
• Sending a network log to support