Nearly all email programs use what’s referred to as POP3 (“post office protocol” for those of you into trivia). That allows email programs to find and retrieve Web-based email from Yahoo! and Hotmail accounts.
But some providers charge for the privilege to access your accounts from an email program.
So try YPOPs for Windows and Mac. This small program enables popular email clients like Outlook, Netscape, Eudora, Mozilla, etc., to download email from Yahoo! accounts. Nifty!