Hello,
If you have a problem with a mail program such as Microsoft Outlook downloading duplicates of all your emails please consider using IMAP instead of POP3:
http://www.emailquestions.com/yahoo-mail/7237-setup-imap-connection-yahoo-mail.html
If you are using a pop3 problem there are a few situations, such as server restores, that can confuse your mail program and cause it to download duplicate emails if you "leave mail on the server".
If you have a problem with a mail program such as Microsoft Outlook downloading duplicates of all your emails please consider using IMAP instead of POP3:
http://www.emailquestions.com/yahoo-mail/7237-setup-imap-connection-yahoo-mail.html
If you are using a pop3 problem there are a few situations, such as server restores, that can confuse your mail program and cause it to download duplicate emails if you "leave mail on the server".