Most users just drag and drop folders around. I think it's dangerous and I'm not confident it will always work. It's ''probably'' OK in POP accounts and the Local Folders account because these are stored locally and are totally detached from any servers. If the move is within an IMAP account, try doing your move via the webmail interface. If you need to do it in Thunderbird, or between two accounts where at least one uses IMAP, I would create the folder structure in the new location (by hand), then copy messages from old to new, one folder at a time. I suggest using the right-click "move to" option. It's more robust and reliable than drag and drop.