Mail download from webmail problem

Hi All,
After download email in my outlook from webmail, the inbox folder of web mail becomes empty of my account. that means, the mails are not copying. they are cut & download. So how can I solve? I mean, from web mail, every mail will be copy in my outlook & the 1 copy will be left in web mail.

Make sure you have the “Leave messages on the server” check-box selected in your Outlook Account setup.