Version: 1.7.9 (using KDE KDE 3.5.7) Installed from: Debian testing/unstable Packages OS: Linux IMAP servers require some backing store for email. There are a number of possible formats, including mbox. The mbox format has a peculiarity: a folder may contain email or subfolders but never both. This is because the mbox format uses different filesystem objects for the two types: folders-with-email folders are stored using files whilst folders-with-subfolders folders are stored as directories. (NB. maildir does not suffer from this.) The direct (non-caching) IMAP account-type within kmail knows this: when creating a new folder, the user is prompted whether this new folder is for containing subfolders or for email. The create folder type is then created, based on the user's answer. The caching (disconnected) IMAP account-type does not ask what type of folder should be created. Instead, newly created folders are allowed to contain both messages and folders. When (re)synchronisation happens, the caching IMAP account-type will attempt to create the new folders. It seems caching-IMAP account-type currently does not support creating folders-with-subfolders folders. Instead, new folders will be folder-with-email type, independent of the folder's actual content. If a newly created folder contains a new sub-folder, the creation of the new sub-folder will fail with a generic "not supported" error message. A work-around is to create a direct (i.e. non-caching) IMAP account for the server and create all necessary folder-with-subfolders folders. Once this is done, further folders-with-email folders can be created using the caching IMAP account-type.
Thank you for taking the time to file a bug report. KMail2 was released in 2011, and the entire code base went through significant changes. We are currently in the process of porting to Qt5 and KF5. It is unlikely that these bugs are still valid in KMail2. We welcome you to try out KMail 2 with the KDE 4.14 release and give your feedback.