If you have trouble creating mail folders, prefix the folder with "INBOX.".
IMP has been upgraded to 3.2, and now supports multiple identities.
This means that to save your sent-mail, after login, you must now go into your "options", "personal information" and "edit your identities", select the Default Identity, and assign yourself a "sent-mail folder".
Other new features include integration with a calendaring application and an improved addressbook.