Outlook completely broken after accidentally marking whole inbox as unread

Hi @Jackson,

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

Regarding your issue, may I kindly ask a few question so I can understand your issue better.  

• Have you tried using Outlook on the Web to see if the issue persists?  
• Have you tried toggling to classic Outlook then toggle back to the New Outlook? 
• Can you provide a screenshot of the issue (make sure you hide all of your personal information) if possible? 

Also, here are a few steps you can try: 

1. Force close and restart Outlook 

Force Close Outlook:  

• Press Ctrl + Shift + Esc to open Task Manager. 
• Find Outlook.exe in the list under the Processes tab. 
• Right-click it and choose End Task. 

Restart Outlook:  

• Click the Start menu or use the search bar. 
• Type Outlook and press Enter to reopen the app.

2. Re-add your account
   This forces the new Outlook to completely rebuild its connection to the server and re-download your entire mailbox from scratch.

• In the new Outlook, go to Settings (the gear icon).
• Go to "Accounts" and find the account that is having the issue.
• Select "Manage" and select "Remove" then follow the steps to remove it.

• Restart Outlook.
• Go back to Settings > Accounts and "Add account" again.

This process will take a very long time, especially with 20,000 emails, as Outlook will have to re-download everything. However, it's the most effective way to ensure a clean, synchronized state.

3. Use Outlook on the Web You can use Outlook on the web as a workaround and to confirm if the issue is specific to the desktop app.
4. Repair Office If the issue is caused by corrupted app files or broken installations, repairing or resetting New Outlook might help resolve it.

• Go to Setting > Apps > Installed apps > Outlook > Advanced options You can choose Repair first and if the issue persists choose Reset. 

Disclaimer: Resetting will remove your configured accounts, app settings, and locally cached data, such as .OST files. However, your emails stored on the server will remain safe. Any manually added .PST files won’t be deleted but may need to be re-added after the reset. 

Hopefully this will help your Outlook work again properly. 

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".  

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread