Hi,
I know you can use procmail without the transport. How I wish sieve can pipe the email to scripts. If you want, I will dig around my test iredmail system for some pointers. I think you have to set the procmail in the postifx and have some way for the procmail to find the user's .procmailrc like nfs mount.
Here is part of the /etc/procmailrc. Please note that I haven't use it on production system. The only thing to note is the SWITCHRC. It is just my hack on the user's home directory. Maybe someone can have a better code. Basically it will process /etc/procmailrc and switch to the user's .procmailrc.
# Set Maildir path.
MAILBOX="/mail/vmail01/$DOMAIN/$USER/Maildir/"
DEFAULT="$MAILBOX"
JUNK="${MAILBOX}/.Junk/"
RECIPIENT="${RECIPIENT}"
SENDER="${SENDER}"
# Variables for vacation.
#VACATION_ON="${MAILBOX}/.vacation.on"
#VACATION_CACHE="${MAILBOX}/.vacation.cache"
#VACATION_LOCK="${MAILBOX}/.vacation.lock"
#VACATION_MSG="${MAILBOX}/.vacation.msg"
#VACATION_SIGNATURE="${MAILBOX}/.vacation.signature"
# Log some message to LOGFILE."
#LOG="--------- Found something. ----------"
# Make sure Maildir exist.
:0
* ? [ -d ${MAILBOX} ] || mkdir -p $MAILBOX
{ }
# Drop spam mail to Junk directory.
:0 H
* ^X-Spam-Status: YES
${JUNK}
SWITCHRC="`/usr/bin/getent passwd $USER | cut -d : -f6`/.procmailrc"
Jacky