I made an export ffrom Outlook .pst to thunderbird and from there to .eml.
All Mails were prperly exported into a folder structure which reflects the Outlook mail folders.
However, after importing, every SINGLE e-mail has its own folder in which the e-mail is then sorted as the only one in this foilder.

I used the built-in kmail "import" utility. Very weird behaviour.

?? Does anyone know another plugin/tool or a setting to correct this (I expect all mails of a topic in one folder.