I get duplicate email on my outlook but not when I web browse

Which version of outlook are you using? What have you done about this far? You night try the Microsoft answer:

This problem may occur if you use the Leave a copy of messages on the server option.

To set the Leave a copy of messages on the server option, follow these steps:

1. On the Tools menu, click E-mail Accounts.

2. Click View or change existing e-mail accounts, and then click Next.

3. Click your POP3 e-mail account, and then click Change.

4. Click More Settings.

5. On the Advanced tab, click to select the Leave a copy of messages on the server check box, and then click OK.

and here is some more

Possible Causes of Duplicate Emails on Outlook Express

Problem: The "Leave Messages on the Server" box has been checked on your Outlook Express account settings.

Fix: Uncheck the "Leave Messages on the Server" box. To do this, click on Tools>Accounts. You will see a box open (named Internet Accounts), click "Mail" tab, click on the mail account, click on Properties>Advanced. Remove the check in the box "Leave a copy of messages on server."

(The following information is from Microsoft Help and Support)

Problem: Outlook Downloads Messages from a POP3 Server Twice Outlook downloads messages from a Post Office Protocol 3 (POP3) server again after it empties the Deleted Items folder even if you have both the Leave a copy of messages on the server and the Remove from server when deleted from Deleted Items options enabled on the POP3 account.

Fix: There is not an available workaround for this problem. . . Simply delete the duplicate messages.

Let us know if this will help....Good Luck