I have specifically *not* subscribed the "Sent" folder or the "All Mail" folder because they're both huge and it slows down my CPU and network too much to keep them subscribed. However, if I send a message, Thunderbird automatically re-subscribes to "Sent", and if I archive a message, Thunderbird automatically re-subscribes to "All Mail". The first attached image is a screen cap of my subscribed folders before sending a message, and the second screen cap is that dialog after sending a message. This seems like a bug because there's no reason that action should signify that I want to re-subscribe to those folders. If I move something to "Sent", I just want it moved on the server side. I do not want to re-subscribe and download the headers of every message in that folder. This has made Thunderbird very difficult to use because it slows down my machine every time I send a message or archive a message, until I go back into the "Subscribe" dialog and un-check those.