Saving archive copy of all mail sent/received w/Dovecot+Postfix?

[Andrew M]

I'm running Dovecot 2.0.15 and Postfix 2.7.7 with postfix handing off to 
Dovecot's LDA.  I am hosting multiple virtual domains with multiple 
users and everything is working.  I would now like to create a permanent 
archive of all sent/received mail with each virtual user's mail saved to 
its own sent file and received file.  This needs to be independent of 
the user's regular Maildir store since he can't delete or modify the 
permanent archive.

Any suggestions on how to best accomplish this either via postfix or 
dovecot?

Postfix has in main.cf

  virtual_transport = dovecot

and in master.cf

  dovecot   unix  -       n       n       -       -       pipe
    flags=DRhu user=virtual:virtual
    argv=/usr/libexec/dovecot  /dovecot-lda -d ${recipient} -f ${sender}

dovecot uses this:

[root@xxx andrew]# dovecot -n
# 2.0.15: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.35.14-103.fc14.x86_64 x86_64 Fedora release 14 
(Laughlin) ext4
auth_mechanisms = plain login cram-md5
disable_plaintext_auth = no
mail_location = maildir:/home/vmail/%d/%n/Maildir
mbox_write_locks = fcntl
passdb {
  args = scheme=plain username_format=%u /etc/postfix/passwd
  driver = passwd-file
}
protocols = imap lmtp
service auth {
  inet_listener {
    port = 12345
  }
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0666
    user = postfix
  }
  unix_listener auth-userdb {
    mode = 0666
  }
}
ssl_cert = </etc/pki/tls/certs/xxx.com.crt
ssl_key = </etc/pki/tls/private/xxx.com.key
userdb {
  args = username_format=%u uid=5000 gid=5000 home=/home/vmail/%d/%n
  driver = static
}

Thanks,
Andrew