I'm switching email providers but I have years' worth of emails with the old account. For unspecified reasons I needed to delete the emails on the server, and I figured this wouldn't be a problem since I had them all locally. I was apparently mistaken about how imap works and I lost all the emails stored in the account locally when I deleted the remote ones.

Fortunately, I have an archive with the emails in it (tar.bz2 file) that I generated using Kmail's Archive Folder option in the right click menu. Unfortunately, the emails are very difficult to access in this format. So I'd like to restore them to an account and just have a dead account in kmail that I can use as repository. But I can't figure out how to do that.

Kmail has Tools > Import/Export KMail Data, which opens up a utility called PIM Data Exporter. But that only wants zip files.

There's also File > Import Messages, but that's greyed out for some reason.

There's also Tools > Import from another Email Client, but that doesn't seem applicable and anyway it wants me to install ImportWizard. And that doesn't seem to be available in Plugins, so I don't know what's going on there.

So... what exactly can I do with this archive file that I have? How am I supposed to make use of it?