When I right-click on a group mail folder and choose "clear cache files" this does not seem to have any effect.

At least I still see "ghost" emails which I already manually deleted from the IMAP-server.

The header line appears in the email list, but when clicking on it, I just get:

From: null
Subject: Either message Removed from Server or moved to a different folder
Date Sent by Sender:
To: null
and

This Message Has No Content
(as the email has been already deleted on the server...)

Does anyone have an idea where the cache entry resides and how to get rid of it?