I have been busy migrating from Windows 7 RC to full retail version of Windows 7. It has taken over 1.5 full days (which includes half a day formatting a brand new 1TB hard drive).
During the course of putting things back onto my speedy fresh install I found a problem when I started up Thunderbird. There were duplicate system folders such as Local Inbox, Sent box, etc. Because they are system folders there is no option to delete. It had been a while since I started it back up from my old install and got some emails in only one of the 2 Inboxes.
After a while I found the problem. It was Dropbox and the way it handles conflicted files / folders.
Take a back up of the profile which contains everything for a user. This includes emails, settings and more. To find where the user profile is go to Tools > Account Settings.
For each account listed click on the Server Settings and at the bottom on the right side of the window there is a textbox with the label Local directory: Copy the directory after ~\Profiles\. Make sure Thunderbird is not running before a copy is taken.
Do not forget to backup the Local Folders too. Select Local Folders and there is a textbox with the same label.
Close Mozilla Thunderbird if it’s still open. Inside the profiles directory there is a folder called Mail. This is where each email account has it’s own folder and there is also the local folder where emails are stored on the computer. Go into each of those folders and look for files or folders where it has the computer name and the description conflicted copy and a date stamp. Check which copy is the latest version (and where the back up may come in handy) using date time stamp of the file, size of the file and the conflict date stamp. Delete the duplicate or remove the original and rename the conflicted file exactly the same as the original file.
A slight pain but it’s worth it if it allows me to access my email offline on multiple computers.