I have the same problem in kmail on hardy.
$ dpkg-query -W kmail kmail 4:3.5.9-0ubuntu3
The inbox is where mail fetched via POP goes (i.e. not an imap one), and poking around in .kde/share/apps/kmail I can't see the message anywhere. But kmail insists that it's there, but I can't read nor delete it.
I have the same problem in kmail on hardy.
$ dpkg-query -W kmail
kmail 4:3.5.9-0ubuntu3
The inbox is where mail fetched via POP goes (i.e. not an imap one), and poking around in .kde/share/ apps/kmail I can't see the message anywhere. But kmail insists that it's there, but I can't read nor delete it.