Please Help! All Messages in Web Email deleted when account added to Outlook

Until now, I've accessed my work email through the online client (it uses a POP server). But earlier today, I added the account to Outlook so that I could see my older emails offline as well.

But after I did this, every single one of my past emails (going back years) was deleted from the online client though I can see all of them on Outlook. This is disastrous, since I need to access my work email from public computers as well.

Please help me transfer my old emails back to the web client!

Thanks very much for your help,
Rachel