New to Kubuntu - I've only had it for a week. This is my first post regarding what appears to me to be a bug.

I setup my primary email address in Kmail. After downloading messages to the inbox, I decided I wanted to sort them into subfolders inside the inbox. So far so good. Then I changed my mind and tried to move the folders outside the inbox. Kmail crashed, and when I opened it again, whenever I try to open one of my folders it says "Local Folders: MailDir (subfolderName) for collection (collectionName) is invalid." I can still see the emails, but I was annoyed at the constant error messages, so I tried to create new directories and move the emails out into new directories.

When I did so, the emails disappeared from the old directory, but didn't arrive at the new directory! Now I was getting angry. Where'd my emails go? I started looking in hidden directories (such as the one listed in the error message), but those were all empty. I finally found them inside Home>.local>share>local-mail>.inbox.directory>(subfolder)

The emails are all there. I can open them with Kmail Viewer. But I can't move them in Kmail, which is scary. I don't want to lose those emails! Some of them are important.

I've noticed the problem is that when I try to open the folder the error says it can't find the a subfolder which is different from the location of the emails on my computer.

For instance the emails are at:
Home>.local>share>local-mail>.inbox.directory>(subfolder)
But it tries to find them at:
Home>.local>share>local-mail>.inbox.directory>(subfolder)>(subfolder)

I fixed the problem by creating a new folder in Kmail, then manually copying the emails (using Dolphin) from the directory where they are to the new directory. Now I can see all my emails in Kmail in the new folder, and I feel confident deleting the old folders. Even so, I'm gonna back up before I do...

Hopefully this will help someone else who runs into the same or similar issue.

I would definitely recommend backing up in this case, it seems that KMail/Akonadi has got itself into an inconsistent state. Which version of KDE are you using? If it is KDE 4.8.4, please file a bug report at bugs.kde.org about this, as it is a potential data loss causing bug.