KMail with mBox format

[Timothy Murphy]

I'm running Fedora-18 with KDE.
I'm accessing mail from the mBox file /var/mail/tim
and this is working fine.
(I was previously trying to access mail from /var/spool/mail/tim
which is linked to /var/mail/tim but that did not work.
Evidently KMail has some problem with linked files?)

The only problem I have now is that mail that I delete with KMail,
eg mail deleted by my spam filter,
is not deleted from the mBox file /var/mail/tim .

Is there any KMail setting that will allow this?
If there is none, is there any way outside KMail of doing this?

It seems incidentally that I cannot include the mBox email
in "Local Folders" on KMail.
This seems to be set to an maildir setup
at /home/tim/.local/share/local-mail ,
which I am not using and as far as I can see cannot delete,
at least within KMail=>Settings .

Maybe I have to do something within System Settings?

Any advice or suggestions gratefully received.