Open your Outlook and follow the steps below to leave a copy on the server, but you will have to delete mails from your webmail account periodically or you overfill your inbox.
On the
Tools menu, click
E-mail Accounts.
Click
View or change existing e-mail accounts, and then click
Next.
Select your ISP account, and then click
Change.
Click
More Settings.
Click the
Advanced tab, and under
Delivery, select the
Leave a copy of messages on the server check box.