Folders become corrupt

I'd like to expand on my previous posting… The "folders" you see in Thunderbird are implemented as files in the file system. So they are subject to the same constraints as regular filenames; I would advise that you avoid any of those characters that have special meanings in filenames, such as *, ?, / and \. I'd also avoid most punctuation marks (I don't KNOW if they do any damage) and stuff like brackets. Now, I don't know for sure if Thunderbird is designed to let you move folders by drag and drop. It seems to work, and I'd be quite confident about it in Local Folders and in POP-connected accounts, as these are all files stored on your own local storage devices. Note also, that under such conditions, if you "move" a file or folder, there doesn't have to be any bulk copying and deleting; the file system just links the item to its new parent. IMAP is a different beast. You are effectively seeing files stored remotely on the server. When you move a file, it is translated into some IMAP commands that tell the server what it is you want to do. The details of how the server does it are not made visible to us; it may do a smart rename/relink thing or it may actually shift bytes. I would hope that whatever you do in the email client is just mirrored in the server, without messages being actually copied up and down your internet link, but who knows? The server is very likely to use a different OS and therefore a different file system, so it may go about things quite differently to how your own computer does it. Note also that in your OS, a drag-and-drop may have different outcomes depending on context. When the source and destination are on the same drive (or volume?) it tends to act like a move. Between different disks or partitions, the default action is to copy. Right-click makes these choices more apparent. So, I don't move folders in IMAP accounts, and specifically, I never move folders between accounts. I'd manually create the new folders then use select/right-click/copy to (or move to) to shift messages. Given that these are all explicit methods shown to us in menus, I can be sure they are intended to work. Drag-and-drop on a folder is an implicit action; the GUI hints that it's possible, but the outcome is not always predictable. I actually use a Thunderbird add-on that pops up a dialogue asking for confirmation if I accidentally try to move a folder, maybe because I've done a clumsy drag-and-drop and missed the message I intended to move, or had one of those increasingly common senior moments where I lose my grip on reality and struggle to remember what it was I came here to do. You ''can ''put your car into reverse gear whilst speeding down the motorway. It's possible but not necessarily useful or productive to do this. I view drag-and-drop of folders as something similar; it's possible but not always a good idea.