dovecot userdb authentication

Hi

I have a remaining issue with a mail server setup.

Composed of Postfix and Dovecote it is is a 'local' mail server
At first I relied upon Mysql to store the various parameters, and then switched to a flat file approach

I also initially set the server up to handle virtual users, but then I realized that it was destined to manage local system accounts only. So I reconfigured it accordingly

Relying on system accounts for authentication means that the domain name component is absent from the username (as opposed to virtual user identifiers)

This caused me some difficulty at first with roundcube, but I was able to get around it through a manual adjustment in Mysql

The remaining aspect that isn't working is the delivery of emails.

The entry in master.cf for dovecot looks looks this:

dovecot   unix  -       n       n       -       -       pipe
    flags=DRhu user=mail:mail argv=/usr/lib/dovecot/deliver -d ${recipient}

The problem is that the recipient equates to the users email address, which can't in fact be used for authentication purposes with system accounts.

I then tried replacing recipient with user:

dovecot   unix  -       n       n       -       -       pipe
    flags=DRhu user=mail:mail argv=/usr/lib/dovecot/deliver -d ${user}

There seems to be a rights issue because I get the following error:

dovecot Fatal: setgid(100(users)) failed with euid=8(mail), gid=8(mail), egid=8(mail): Operation not permitted

Any ideas ?

thanks

yann