[exim] Heaving local mail from the mail-client to exim

Hello everyone !

I got in touch with exim4 yesterday so I'm new to this list.
This may be a very simple question, but ... :

I configured exim4 on my debian-sarge to deliver mail via smtp to a
smarthost.
Sending mails on the console works almost perfectly, including
authentication and encryption.

What I didn't figure out so far: How can one point exim to the my
mail-clients outbox-directory, to take these mails and deliver it to the
smarthost ?
As I read in the exim-intro, a spool directory is a special exim
directory, not the local client-mailbox.
Kmail detects exim's ssl-capabilities (localhost:465), but I couldn't get
them to exchange mails.
Further reading of docu and grepping the inet did not lead me to a
solution, so I greatly appreciate your help.

Thanks,
Michael