If your going to use windows to search for files, you must tell it to display hidden files and folders.

see http://windows.microsoft.com/en-au/windows/show-hidden-files#show-hidden-files=windows-7

But it is more likely your anti virus is the issue. disable email scanning and allow the download to complete, before you think of re-enabling it. Duplication of email used to be discussed on the Symantec support forum, but I must have linked to it to many times. They removed it.

It doesn't appear to be anti-virus related- but thanks anyway. Seemed to have solved problem now of downloading the same emails. Located popstate.dat file in the profile, renamed it as popstateold.dat Exited Thunderbird- When reopened TB automatically created a new popstate.dat file Tested it out by reopening TB several times. Now my most recent emails have only downloaded the first time and not every time TB reopened This might help others with the same problem.

Great you have it working, but think about what would have caused the file to not update correctly in the first place before you discount anti virus.

I've been having the same problem since 04.16.2014 with both of my email accounts, whether I'm running the default add-ons (which are up to date) or not. My antivirus does not include email scanning (verified with developers). I do not have any 3rd party programs dealing with email that I'm aware of. I also do not have a file called 'popstate.dat'. I have not personally installed any add-ons, but there are 11 plug-ins; 8 active and 3 disabled. It doesn't happen all the time, but it does happen daily anywhere from 1 - 6 times. There is no extra process running when it happens, nor is there an extra process running when it doesn't. I was hoping the next update would solve it, but that did not happen. Win7 Home x64; TB = Ver. 30 (at the moment). Anything else I can try short of a reinstall, or a product alternative?

re: 'I also do not have a file called 'popstate.dat'.'

I think you may mean that you have not located it. It is a hidden file, so you need to make hidden files visible first.

make hidden files visible:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

Profile folder extra info:

• http://kb.mozillazine.org/Profile_folder_-_Thunderbird

In Thunderbird

• Help > Troubleshooting Information
• click on 'Show Folder' button
• a new window opens showing your Profile folder

• Close Thunderbird now
• click on 'Mail' folder
• click on the 'mail account name'
• scroll down and locate 'popstate.dat' a DAT File.
• Delete 'popstate.dat'
• close the window - top right X

• Open Thunderbird

This will create a new popstate.dat file. As it is empty, it will look at server Inbox and download everything that is in the server Inbox. But it should only do this once. then remove the duplicate emails.

see image to help locate popstate.dat file

I had the same problem with getting 2 or 3 copies of the same email and I tried all the recommended troubleshooting including compacting folders (and set it to compact more frequently), and deleting the .msf and popstate.dat files and this did not fix the issue.

I then permanently disabled the email scan on my Avast antivirus (as well as deselected the monitoring of it to eliminate the annoying warning) and now everything is fine. No more duplicate emails. So in my case it was the antivirus. Thanks!