Windows 7 with Outlook 2003, then 2007 & now 2010 (not Exchange). Three separate POP3 accounts from same ISP. Only one of the three accounts downloads duplicate email messages. Outlook 2003; 2007 & 2010 also ran/running on XP and Vista did not/do not have this problem - only with Win 7. Modifying delivery options corrects the problem, but stops delivery to the other computers on my LAN.

Would you be able to use IMAP rather than POP, as this newer protocol should alleviate the issue. If not, or if your mail provider does not offer it, I would suggest checking the account settings. Since only one account does this, it must be a difference in the account setup (either on the email server, or how the email account is configured within the email program's account settings). Note that POP is very susceptible to duplicate downloads, so after you make changes, you'll likely need to clear the account directory, erase all messages that have been retrieved, and initiate the account again. If this was helpful, please vote by clicking the green triangle. If it solves the issue, click Propose as Answer. Thanks!

The account settings were unchanged because all accounts were set up by importing iaf files exported from previous versions. Outlook 2003 was on two XP Pro desktops and one Vista Home Premium (SP2) laptop with no problems for several years. Reconfigured one desktop to Win 7, loaded Outlook 2003 and discovered the duplication occurring during each and every download to that single account (all 3 accounts from same ISP - Comcast). Deleted wayward account and manually reinstalled it with no change. Deleted it again and reinstalled by importing iaf, again no change. I installed Outlook 2007 on all three computers with no operational changes to any of them. Then I loaded Office 2010 on the Win 7 desktop and Vista laptop with no operational changes to either. I did an item by item Outlook configuration comparison and imported all the email account configurations to assure commonality of installations. The duplication only occurs on the one email account and only on Win 7. That same account also downloads to my Blackberry with no duplication. From my limited perspective, the only variant I can see is Win 7.ArnHedd

If all three accounts are from the same ISP and configured identically, if it was Windows' fault, it should happen to all three. Since two of them work fine, I would think the issue has to be in that 3rd account, somehow. I know it can't be interference from the other computers/email programs, because POP is one-way communication only. I'm not sure what to check though. I know some programs have a "keep email on server after download" or similar option, but you need that in your case so your other computers/email programs can get the mail. Although IMAP would solve that, it may not be a viable solution for your needs. If this was helpful, please vote by clicking the green triangle. If it solves the issue, click Propose as Answer. Thanks!

Changing the server delivery configuration to "delete on download" solves the problem, but also keeps the email from downloading to the other two machines. There is a fourth account too that does not have the problem either. It's a Gmail account that I added when Comcast reduced their limits on the email file size - I often have file attachments in the 10 to 15MB range and email attachments are much easier and quicker than the ftp hassle. It's frustrating, but easily solved by eliminating the offending account. Hitting the delete key is a minor inconvenience - not knowing the cause or solution is the real frustration. I kept adding email accounts over the years in feeble attempts to fight spammers, so eliminating one is really insignificant.ArnHedd

Gmail has the benefit of IMAP instead of POP, which is 2-directional syncing of email. This way all your computers can have the exact same messages all the time. If you download mail to one computer and move it to a folder, it gets moved to that same folder on all other computers (and the gmail website), automatically. It might save you some headache. If this was helpful, please vote by clicking the green triangle. If it solves the issue, click Propose as Answer. Thanks!