To get WinGate to download mail from your ISP POP3 account, you need WinGate 6.0 (any beta), and you add a POP3 collection item.
This then allows you to set up the ISP server for collecting mail, the account name and password, and what to do with the mail you download.
You will first need to create a local domain though. Probably this will be the same domain name as the mail you receive at your ISP - it depends on how your mail is set up at your ISP.
For example a common scenario is: your ISP hosts an entire mail domain for you e.g. yourdomain.com. All mail for that domain goes into a POP3 account at your ISP.
In this scenario, you would set up a local domain called "yourdomain.com", and specify that it is hosted locally. Then any mail for
anyone@yourdomain.com that WinGate gets its hands on (either by receiving from an email client on your LAN, or by downloading from your ISP with POP3 collection) will be delivered into your local mailboxes.
Then for your POP3 collection, when you specify how to deliver mail that is retrieved, you would tell it to deliver to any matching local domain.
The POP3 client in WinGate will then download the mail, look up the destination addresses (to: and CC: fields), and look up the domains associated with those addresses. If they match a local domain (which they will if you set one up), then that is where the mail will be delivered.
Adrien