Please check to see if you have a program like CCleaner. It can cause havoc with Thunderbird files by deleteing them.

It can delete pasword files, session files and popstate.dat files etc

Do not let CCleaner or similar product have access to any trhunderbird file or folder.

Also try this:

• Create folder.
• Move all good emails from Inbox to new folder.
• Delete any emails you do not want.
• Right click on Inbox and select 'Compact folder'

Usually you do not need to empty Inbox in order to compact a folder, but if there is any corruption suspected, then at least you will not lose any emails.

• Right click on Junk (or Spam) and select 'Empty Junk'
• Right click on Junk (or Spam) and select 'Compact folder'

I have CCleaner but have not run it in a long time and it is not set to automatically run. I also have Ashampoo WinOptimizer, however it does not have any settings for Thunderbird, but I stopped it from optimizing Firefox just in case there was any overlap.

As far as Compacting the Inbox, I have numerous sub-folders in my inbox. Do I need to move all of the folders out as well? And if so, will that break my filters?

Thanks.

Subfolders of Inbox will be ok as they are in a different mbox file.

If you are running Ashampoo WinOptimizer then it is possible that it is the culprit.

You do not want any type of cleaning program having access to any Thunderbird file or folder. Pop mail accounts use a 'popstate.dat' file which is in your Thunderbird profile mail account folder. C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\<Profile name>\ Mail\<pop mail account name>

The 'popstate.dat' file keeps a record of everything you have downloaded in the past so that it does not download again. If that file is deleted, a new one is created. Anything which is currently still in your server Inbox is likely to get downloaded again. This can create duplicates and make some deleted items reappear.

There are various session, cache, password and a host of other files which you do not want other programs having access.

I do not use the program you mention, but with these types of program, usually you have to make exceptions to stop them accessing eg: Thunderbird files and folders.

If Ashampoo WinOptimizer is not the culprit: I also mentioned the emptying and compacting of Inbox, because if the file has become corrupted for some unknown reason, then previously downloaded/deleted mail can reappear. Note I mention 'reappear' and not 'download again'. So if you do the moving, deleting and compacting of Inbox folder this will resolve that issue. It is worth doing as a precaution, but if Ashampoo WinOptimizer has access to any Thunderbird folder then you may still get various issues.

I stopped Ashampoo WinOptimizer from clearing Firefox Data (there was no setting for Thunderbird) and so far I have not gotten any duplicate emails since.

Thanks Toad-Hall

If it starts happening again I'll try compacting the inbox.

Update info: Would you be talking about an old verizon account which has recently moved to aol ?

If yes, then you are not the only person experiencing old messages being downloaded again. Recently. I've come across a few people who are talking about duplicates and they mention aol and old verizon account.

Thinking out a loud...but...It is almost as if old messages on verizon server are being transfered over to aol server Inbox and therefore being seen as new mail to download.

No. It has been AOL since the beginning. I'm so far convinced it was Ashampoo that was causing the problem. Ever Since I reconfigured it, I have stopped getting duplicate emails.