Start with the right checks.
A quiet inbox can mean a delivery, storage or display issue. Compare a known test message and avoid changing many mail settings at once.
What to do next.
Check whether sending works and whether the account shows a storage or quota notice.
Ask a trusted sender for a harmless test and any rejection message they receive.
Review Junk and other expected folders, along with inbox filters.
Use Microsoft’s Outlook.com guidance for the exact error and check whether the problem affects more than one device.
Check the result.
Find the test message or obtain its rejection details. If storage blocked delivery, a sender may need to resend after the issue is resolved.
Stop and get help if…
The account has unexpected rules, unfamiliar changes or a persistent delivery error. Get help reviewing the cause before deleting large amounts of mail.