[Dovecot] Mail logger question

[Hungerburg]

I use Dovecot simply as a way, to provide an e-mail archive for people 
on the LAN, where they can move messages into from within thunderbird. 
Mails are stored in a maildir of one system user where all the people 
know the password of. This was very easy to setup in ubuntu 12.

Today I started using the mail_log plugin to provide an audit trail. Now 
I am looking for a light way, to get the log reflect the different 
people or principals.

One way is, to create users with the same ID in the passwd and shadow 
files, but I'd rather have them in a separate file, something like a 
list of aliases for the system user.

Can you suggest a simple way, without going virtual users?

Below the relevant info on dovecot:

$ dovecot --version
2.0.19

$ dovecot -n
# 2.0.19: /etc/dovecot/dovecot.conf
# OS: Linux 3.2.0-35-generic x86_64 Ubuntu 12.04.1 LTS
mail_plugins = " fts fts_squat mail_log notify"
passdb {
   driver = pam
}
plugin {
   fts = squat
   fts_squat = partial=4 full=10
   mail_log_events = save delete undelete expunge copy mailbox_delete 
mailbox_rename
   mail_log_fields = uid box msgid size from subject
}
protocols = " imap"
ssl_cert = </etc/ssl/certs/ssl-cert-snakeoil.pem
ssl_key = </etc/ssl/private/ssl-cert-snakeoil.key
userdb {
   driver = passwd
}

Thank you all

-- 
peter