http://kb.mozillazine.org/Outbox

Thanks for the link but still doesn't fully answer my question. There is an "Outbox" folder in my Local Folders. There is also an "OUTBOX" folder in my GMX account in Thunderbird and an "Outbox" folder also in my Hotmail account. Yet there is none in my Gmail account.

If it for unsent messages until they send, why would it not be in all the accounts? Also why do they have different names?

I notice that gmail and Hotmail, when viewed on their websites, do not have an Outbox, but rather scheduled sending, so that at least explains why you can't subscribe to an outbox for gmail in TB. I don't know why Hotmail accounts show an Outbox. So, the Outbox in TB exists to fulfill the Send Later function of TB, for accounts that don't work exactly in that way. TB also has scheduled sending, provided by the Send Later add-on.

Thanks... that explains part of it. It is also weird how they are named a big different, with the GMX one being all caps

I don't remember seeing these folders in older versions of TB, so is this a "new" addition?

The Outbox has always been part of TB, but if you had POP accounts instead of IMAP, the only outbox would have been under Local Folders.

I'll have to boot up an old laptop with and old version of TB on it (50 something) and see if that had it in there as well. I know it was using IMAP as well for those accounts.