Got an email from a family member in regards to their Thunderbird. They switched ISP and email providers and when their email account was setup in Thunderbird, it had its own folder structure. My first thought was the account had been setup as IMAP, but I checked on the provider’s website determined they didn’t support IMAP.

I thought may be this was they way Thunderbird 3 handled POP accounts. Wouldn’t really know since I use IMAP exclusively. After a little hunting I discovered you can still have Thunderbird to deliver all the messages in your POP accounts to the Global Inbox (in the Local Folders).

Important: Copy all your messages in that account including those in the Inbox and any other folders (sent, drafts, etc) to the Inbox (and other desired folders) under local folders. After that is done, follow these steps:

1. Go to Tools >> Account Settings
2. In the list locate the POP account you want to change the settings on and click on Server Settings (directly below the account name)
3. Click the Advanced… button towards the bottom right
4. In the pop-up windows select Global Inbox (Local Folders Account)
5. You will get an overly worded warning message about losing existing content if you haven’t already copied it to the local folders. Press OK
6. Press OK again to close out of the Account Settings window
7. Restart Thunderbird to remove the separate folders associated with that email account.

For more information see: mozillaZine: Global Inbox