1. Check whether you are viewing emails in a preview pane. If so, try to disable the feature by changing the view settings.
2. Confirm the ‘unread’ filter is set correctly. If not, reset the filter to read all your emails.
3. Look for message delivery settings that limit the number of emails you can view. If present, increase the limit to all emails.
4. Ensure your mailbox size is within the desired quota settings. If not, you may need to clear unwanted emails from your mailbox.