I used the system upgrade to Panther for a full backup and a clean Panther installation. Therefore, I had to import my old e-mails back to Apple Mail. Apple Mail puts all imported e-mails in a folder called "Imported" (or something similar - I use the German version), so I had to move them manually to the desired locations. Everything worked fine, except for the Inbox folder: I always got an error message that I cannot put my mails in there. Well, the problem can be solved easily:
- Just create a new mail account using Preferences -> Accounts and enter some values. It does not need to be a working account.
- Notice that in the folder pane on the right side, there are now two subfolders of the Inbox, one for each mail account. Dragging my old mail directly into one of these subfolders worked without any complaints.
This problem seems to exist only if you use just one mail account.