How to get dovecot to use postfix mailbox?

I try to get postfix and dovecot up and running.

I have a little problem with the mail-box path that connects both.

Postfix

virtual_mailbox_base = /var/vmail virtual_mailbox_domains = mydom.org 

This creates a file

/var/vmail/mydom.org/sam 

as an mbox-file if I send to [email protected]. The sent mail is inside of that file.

So far - so good.

But in dovecot I have this for a virtual user.

[email protected]:{PLAIN}mysecret:5000:5000::/var/vmail/mydom.org::userdb_mail=mbox:~/%u 

That creates

/var/vmail/mydom.org/[email protected]/inbox 

after successful login.

So my POP3-client finds always an empty mailbox. If I copy the postfix-mailbox to the inbox-file, then POP3 gets the message.

How do I get dovecot to use the postfix-mailbox or postfix to use the dovecot-file? I tried several settings in dovecot but I did not get it going to use the posfix-file as it is.

Thanks!