How To Automatically Add A Disclaimer To Outgoing Emails With alterMIME (Postfix On Debian Squeeze)
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This tutorial shows how to install and use alterMIME. alterMIME is a tool that can automatically add a disclaimer to emails. In this article I will explain how to install it as a Postfix filter on Debian Squeeze.
1 Preliminary Note
I'm assuming that Postfix is already installed and fully functional - I will not explain how to set up Postfix and configure email accounts in this tutorial.
2 Installing alterMIME
alterMIME can be installed as follows:
apt-get install altermime
Next we create the user filter with the home directory /var/spool/filter filter - alterMIME will be run as that user:
useradd -r -c "Postfix Filters" -d /var/spool/filter filter
mkdir /var/spool/filter
chown filter:filter /var/spool/filter
chmod 750 /var/spool/filter
Afterwards we create the script /etc/postfix/disclaimer which executes alterMIME. Debian's alterMIME package comes with a sample script that we can simply copy to /etc/postfix/disclaimer:
cp /usr/share/doc/altermime/examples/postfix_filter.sh /etc/postfix/disclaimer
chgrp filter /etc/postfix/disclaimer
chmod 750 /etc/postfix/disclaimer
Now the problem with this script is that it doesn't distinguish between incoming and outgoing emails - it simply adds a disclaimer to all mails. Typically you want disclaimers only for outgoing emails, and even then not for all sender addresses. Therefore I've modified the /etc/postfix/disclaimer script a little bit - we'll come to that in a minute.
Right now, we create the file /etc/postfix/disclaimer_addresses which holds all sender email addresses (one per line) for which alterMIME should add a disclaimer:
vi /etc/postfix/disclaimer_addresses
[email protected] [email protected] [email protected] |
Now we open /etc/postfix/disclaimer and modify it as follows (I have marked the parts that I've changed):
vi /etc/postfix/disclaimer
#!/bin/sh
# Localize these.
INSPECT_DIR=/var/spool/filter
SENDMAIL=/usr/sbin/sendmail
####### Changed From Original Script #######
DISCLAIMER_ADDRESSES=/etc/postfix/disclaimer_addresses
####### Changed From Original Script END #######
# Exit codes from <sysexits.h>
EX_TEMPFAIL=75
EX_UNAVAILABLE=69
# Clean up when done or when aborting.
trap "rm -f in.$$" 0 1 2 3 15
# Start processing.
cd $INSPECT_DIR || { echo $INSPECT_DIR does not exist; exit
$EX_TEMPFAIL; }
cat >in.$$ || { echo Cannot save mail to file; exit $EX_TEMPFAIL; }
####### Changed From Original Script #######
# obtain From address
from_address=`grep -m 1 "From:" in.$$ | cut -d "<" -f 2 | cut -d ">" -f 1`
if [ `grep -wi ^${from_address}$ ${DISCLAIMER_ADDRESSES}` ]; then
/usr/bin/altermime --input=in.$$ \
--disclaimer=/etc/postfix/disclaimer.txt \
--disclaimer-html=/etc/postfix/disclaimer.txt \
--xheader="X-Copyrighted-Material: Please visit http://www.company.com/privacy.htm" || \
{ echo Message content rejected; exit $EX_UNAVAILABLE; }
fi
####### Changed From Original Script END #######
$SENDMAIL "[email protected]" <in.$$
exit $?
|
Next we need the text file /etc/postfix/disclaimer.txt which holds our disclaimer text. Debian's alterMIME package comes with a sample text that we can use for now (of course, you can modify it if you like):
cp /usr/share/doc/altermime/examples/disclaimer.txt /etc/postfix/disclaimer.txt
Finally we have to tell Postfix that it should use the /etc/postfix/disclaimer script to add disclaimers to outgoing emails. Open /etc/postfix/master.cf and add -o content_filter=dfilt: to the smtp line:
vi /etc/postfix/master.cf
# # Postfix master process configuration file. For details on the format # of the file, see the master(5) manual page (command: "man 5 master"). # # Do not forget to execute "postfix reload" after editing this file. # # ========================================================================== # service type private unpriv chroot wakeup maxproc command + args # (yes) (yes) (yes) (never) (100) # ========================================================================== smtp inet n - - - - smtpd -o content_filter=dfilt: [...] |
At the end of the same file, add the following two lines:
[...]
dfilt unix - n n - - pipe
flags=Rq user=filter argv=/etc/postfix/disclaimer -f ${sender} -- ${recipient}
|
Restart Postfix afterwards:
/etc/init.d/postfix restart
That's it! Now a disclaimer should be added to outgoing emails sent from the addresses listed in /etc/postfix/disclaimer_addresses.
3 Links
- alterMIME: http://pldaniels.com/altermime/
- Postfix: http://www.postfix.org/
- Debian: http://www.debian.org/
