1. Check your Outlook settings for any filter applied that could be preventing you from viewing all emails
2. Test to see if you can view emails on a different device or computer
3. Clear out your cached Outlook data and preferences
4. Remove unreliable accounts or connections from the Outlook software and re-connect them
5. Make sure that Outlook and Windows are up to date
6. Disable any add-ins or third-party extensions that may interfere with Outlook
7. Use the Outlook Inbox Repair Tool