[Dovecot] Dovecot does not access /var/mail when using Maildir

[mirko at mirkonet.nl]

Hello,

I'm running debain on my machine with postfix, squirrelmail and dovecot
installed. Everything works fine and I'm able to access my mail via
squirrelmail and via Outlook with imap.
However I want to create subfolders what is not possible. After reading I
discovered that I use mbox and that maildir is needed in order to be able
to use subfolders.
I have created a Maildir folder with the  maildirmake.dovecot command in
my /home/mirko directory and corrected the owner.
Now dovecot uses the Maildir and I can create subfolers. However my
problem is that I don't receive Emails in my Inbox. Incoming mails are
delivered to /var/mail/mirko, but when dovecot uses Maildir it doesn't
access this. I have played with the default_mail_env settings in
dovecot.conf which does influence the use of mbox or Maildir. However the
problem remains: As soon as Maildir is used, the Inbox is empty and I
don't receive Email.

Is there a way when Maildir is used to point dovecot to /var/mail/ for the
incoming Email? Or do I something else wrong?
Your help is appreciated.

Greetings,
Mirko