Missing or Deleted Messages in Microsoft Outlook
No panicking allowed. For the most part, this is caused by a view that you have set and didn't realize it. Outlook doesn't just arbitrarily start deleting emails. Good news, right?
There's two reasons this occurs. There could be more.
You've assigned a home page to your Inbox.
Right-click your Inbox and choose Properties. Click on the Home Page tab and delete anything that's in the Address box.
You're not viewing all messages.
Go to View Toolbars and choose the Advanced Toolbar.
From the Current View drop-down, choose Messages. Likely, you're only viewing unread messages or something else.