Description of problem:
Since RHEL4 ships with a default mail environment that uses mbox with dovecot,
dovecot should be configured to have this configuration as default in
/etc/dovecot.conf:
mail_extra_groups = mail

Version-Release number of selected component (if applicable):
dovecot-0.99.11-2.EL4.1

How reproducible:
having imap as a backend



Steps to Reproduce:
1. Create a new user with an ldap backend 
2. check your email using dovecot imap
  
Actual results:
- you see in /var/log/maillog:
Apr 19 10:45:16 iserver imap(username): open(/var/mail/username, O_CREAT)
failed: Permission denied


Expected results:
the file /var/mail/usernam is created

Additional info:
The issue is solved by configuring en /etc/dovecot.conf
mail_extra_groups = mail