I have been using T-bird for over 15 years, and somewhere during a migration in the past I wound up with 2 In boxes. One is located at top of tree under email name. The other is located just under Local folders. It is the same way on 2 of my desktop and laptop. Only one under local folders will have current emails and I believe all emails., while the other has older emails, that at one time were current and I was using it as well. inbox 2 in local folders is currntly the one I use and it has 17k emails in it , and inbox 1 under email name has 4 k in it. Also when I come back to desktop after being out of town for couple of weeks, none of my work (deletions /new folders sinc between computers. However as soon as i boot up T-bird in desktop, it downloads every email that came in while I was gone, even the ones I have already deleted on the laptop. I also have 2 sent and trash boxes. It is important that I don't loose any emails, so I have been tolerating it for a long time.