Hi,
What type of email account are you using?
Have you tried starting Outlook with /cleanviews switch? Exit Outlook, press Windows key + R to open the Run command, type outlook /cleanviews and press Enter.
Please also try logging into the webmail client and check if you can see the test email in the Inbox. If you can see all email from webmail access, we can also try create a new subfolder under Inbox from webmail, move all emails from Inbox to the subfolder. Then, check your Outlook to see if you can see the emails in the newly created subfolder. If so, try moving all emails back to Inbox to see if the emails will disappear again.
Please let me know the result.
Steve Fan
TechNet Community Support