[exim] The appendfile transport: UID and GID of the delivery…

Hello buddies,

I need message file have a specific UID and GID after delivery process,
in special environment:

Exim is running with a non-root user (UID: exim) and group (GID: exim)
and the exim binary is without setuid permission: -rwxr-xr-x.

The transport configuration is:

maildir:
     driver = appendfile
     maildir_format = true
     create_directory = false
     directory = /var/mail/LBN/$domain/$local_part
     mode = 0660

The maildir was create apart with follow permissions, uid e gid:

drwxrws--- exim <group> /var/mail/$domain/$local_part/cur
drwxrws--- exim <group> /var/mail/$domain/$local_part/new
drwxrws--- exim <group> /var/mail/$domain/$local_part/tmp

<group> - a unique gid defined to each mail address

I should like that file create to store delivery message owned "exim
uid" and "<group> gid", but exim delivery process makes with "exim uid"
and "gid exim". In fact, I need exim process does not set any uid and
gid leaving this responsability to SO.

I appreciate any suggestion.

-- 
     Ednardo Lobo

     www.lobo.eti.br