Outlook Desktop Old Calendar Notifications Popping up

Question

Outlook Desktop keeps showing old calendar reminders that I have already dismissed. In addition, my email stops syncing regularly, and I have to close and reopen Outlook every 1–2 hours to get new emails to download.

Troubleshooting steps I’ve already tried:

• Signed out of Outlook and signed back in
• Ran outlook.exe /cleanreminders
• Used MFCMAPI to delete the Reminders folder, then ran /cleanreminders again
• Resynced my Microsoft 365 account
• Reinstalled Outlook completely

Despite these steps, the problem is still happening. Has anyone experienced this or know what else I can try?

Answer 1

Hi @Janet Blanchard

Thank you for posting your question in the Q&A Forum. 

Based on what you’ve done, it seems the old calendar reminders are not just a local glitch in Outlook. Since MFCMAPI didn’t resolve the issue, it’s likely caused by corruption in the mailbox index on the server side.

Here are the recommended steps:

1. Create a New Outlook Profile

Creating a new Outlook profile forces a fresh download of your mailbox and can resolve issues caused by a corrupted local cache. You can follow Microsoft’s official guide here: Create an Outlook profile - Microsoft Support

Note: If reminders continue to appear in the Outlook Web App (OWA), you can skip this step as it confirms the issue is strictly server-side.

2. Mailbox Rebuild / Move

At this point, the most reliable approach is to ask your IT admin to perform a mailbox move or rebuild. This process recreates the mailbox index on the server, clearing any corrupted reminders that local tools cannot remove. Once completed, reminders should stop, and mailbox sync should stabilize.

While local steps like /cleanreminders are helpful, a server-side rebuild is often the only way to fully resolve persistent reminder corruption. Please ensure all important data is backed up beforehand, though this procedure is generally a safe and standard administrative task.

Hope this clarifies the options and next steps.

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Answer 2

It sounds like you're experiencing persistent issues with old calendar reminders in Outlook and email syncing problems. Since you've already tried several troubleshooting steps, here are a few additional suggestions:

1. Clear Offline Items: You can try clearing offline items from your calendar folder. Right-click the affected calendar, select Properties, then choose Clear Offline Items. After that, select Send / Receive > Update Folder to force a download of the items from the server.
2. Check Group Policy Settings: If reminders are not displaying properly, it could be due to Group Policy settings. Ensure that the option to display reminders is not disabled either in the Outlook user interface or through Group Policy.
3. Registry Check: If you're comfortable with it, you can check the Windows registry to ensure the reminder display setting is correct. The key is located at HKEY_CURRENT_USER\software\microsoft\office\<x.0>\Outlook\Options\Reminders. Ensure the DWORD value is set to 1 to display reminders.
4. Repair Outlook: If the problem persists, consider running a repair on your Outlook installation through the Control Panel.
5. Check for Updates: Ensure that your Outlook application is fully updated to the latest version, as updates can resolve bugs and improve performance.

If these steps do not resolve the issue, it may be beneficial to reach out to Microsoft Support for further assistance.

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References:

• Calendar reminders in Outlook can't be dismissed or keep reappearing
• Reminders in Outlook do not appear