This may be due to another issue and not simply because you leave the mail on the IP server. Some of it depends on what software you are using like MS OutLook, MS Office...
http://www.pcworld.com/downloads/tc/...utilities.html Try search box and enter duplicate email and you'll see there are choices but they shareware. You can try freeware libraries and see if a kind soul has one but I didn't see one.
Take a look over here> What to Do When You Receive Duplicate Messages in Outlook Express
A corrupted email(s) may be causing the problem.
This is a very sad tale of duplicates and even triplicates from business people who are on an MS Exchange email server.
Just a note; I personally do not use any email software, nada, none. I use the email provided on the server from my IP provider which happens to be Verizon and freebe gmail. There are two reasons for this;
1. It's much harder to download viruses or malware, it stays on the IP server.
2. I really don't want a bunch of email clogging up my laptop hard drive even if it is compacted, it still creates problems over time with number of names. Those auto downloads (Office Express, OutLook); suck everything and just slap it down on your PC. I think I would use Mozilla's Thunderbird email if I really had to use a package.
I hope someone has a simpler answer for you. The more tricks any device can do with just a point and click only means under the covers it is very complex. Come back and let us know how you are doing.
You, O LORD, keep my lamp burning; my God turns my darkness into light. Ps. 18:28