This script writes emails piped from postfix into separate files.

mail_write_script.sh

#!/bin/bash
#
# This script writes emails piped from postfix into separate files. It also removes
# new line delimiters which causes issues when viewing in Outlook.
#
# Setup:
#
# It requires lines in master.cf that looks something like this:
#
# to_filesystem    unix  -       n       n       -       -       pipe
#   flags=FR user=emailuser argv=/root/mail_write_script.sh ${recipient} ${queue_id}
#
# And for main.cf to route to this output, e.g:
#
#   default_transport = to_filesystem
#
# Finally, a user called "emailuser" will need to be able to execute this script and write to the 
# directory /opt/mail.
#
# Script:

# read from stdin

DATA=$(cat)

# variables passed from postfix

RECIPIENT=$1
QUEUE_ID=$2

# remove =\n and replace with \n

PARSED=$(echo "$DATA" | sed ':a;N;$!ba;s/=\n//g')

# calculate directory

DESTINATION_DIR=/opt/mail/${RECIPIENT}_${QUEUE_ID}.eml

echo "$PARSED" > "$DESTINATION_DIR"