Update: it's not a mailbox limit, it's some individual messages. Most (perhaps all) seem to have the icon used for draft messages (showing a pencil). I'm not sure quite how or why they're in an Inbox, but they are. Many appear to be old drafts, but some are from other people but have a blank sender ID or for some other reason seem uncopyable to anything but a purely client-side folder.
If anyone can think of a way to filter/sort these messages it would be useful.
I've been copying messages between two accounts using Zimbra Desktop, but I seem to have hit a limit somewhere along the line. When dragging messages over the destination folder it is normally highlighted and the drag icon changes from red to green, indicating a valid drop target. However, I'm now finding that I can't drop the next bunch of files - the target folder isn't highlighted and the drag cursor remains red, unless I reduce the number of files being dragged.
Presumably there's a limit somewhere that's causing this behaviour. I've tried creating a new folder in the target mailbox but that behaves exactly the same, so it doesn't seem to be a folder limit. Is there a limit somewhere in Zimbra Desktop (v2.0.1), or is it likely to be picking up something from the IMAP server (hMailServer, v5.3.3)?