This documentation is based on the Linux distribution I used (Red Hat 9 with Postfix), and although it should work on most any Linux distribution, you may need to defiate from the exact instructions to get it working on your particular flavour of Linux.
alterMIME can be downloaded from http://www.pldaniels.com/altermime/. The version I used was 0.3.1.
Once downloaded, you need to unpack the tarball, change into the new directory and run
make
After building the altermime executable, install it as follows
cp altermime /usr/bin/ chown root.root /usr/bin/altermime chmod 755 /usr/bin/altermime
Unless you have already done this to run other filters in Postfix, the next step is to add a user account to the system that Potfix will use to run the alterMIME filter
useradd -r -c "Postfix Filters" -d /var/spool/filter filter
Once you have created this account you need to create the account's home directory
mkdir /var/spool/filter chown filter.filter /var/spool/filter chmod 750 /var/spool/filter
You now need to create the following script, changing whatever you need to personalize it
/etc/postfix/disclaimer
#!/bin/sh
# Localize these.
INSPECT_DIR=/var/spool/filter
SENDMAIL=/usr/sbin/sendmail
# 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; }
/usr/bin/altermime --input=in.$$ \
--disclaimer=/etc/postfix/disclaimer.txt \
--disclaimer-html=/etc/postfix/disclaimer.txt \
--xheader="X-Copyrighted-Material: Please visit http://www.company.com/privacy.htm" || \
{ echo Message content rejected; exit $EX_UNAVAILABLE; }
$SENDMAIL -oi "$@" <in.$$
exit $?
Once you have created this script, set the permissions to allow it to be executed by the filter user
chgrp filter /etc/postfix/disclaimer chmod 750 /etc/postfix/disclaimer
You need to create the disclaimer text file that was specified in the disclaimer.sh file
/etc/postfix/disclaimer.txt
The content of this file is very much dependent on your requirements, but examples can be found at http://www.emaildisclaimers.com.
In my situation, I have used the same file for both the --disclaimer and --disclaimer-html
files. I tried to use the --htmltoo parameter to tell alterMIME to use the same file for both, but
this did not seem to work correctly.
Finally, you need to configure Postfix to run the filter. In my case, I only wanted outgoing messages to be modified, so I explicitly configured Postfix to listen on different network interfaces, but to only run the filter on the one.
To achieve this, you need to modify the smtp service in etc/postfix/master.cf/ to be as follows
<incoming ip>:smtp inet n - y - - smtpd
<outgoing ip>:smtp inet n - y - - smtpd
-o content_filter=dfilt:
replacing <incoming ip> and <outgoing ip> with the IP addresses of the different network interfaces. In practice, these IP addresses could be bound to the same network controller.
Now you need to add the following new service to the same file
dfilt unix - n n - - pipe
flags=Rq user=filter argv=/etc/postfix/disclaimer -f ${sender} -- ${recipient}
NOTE: You need to ensure that local processes are still able to send mail. The simplest case way is to include
a line like the one below in etc/postfix/master.cf/ (Thank you to Ian Clancy for pointing out this omisson).
127.0.0.1:smtp inet n - y - - smtpd
Once you have done this, restart Postfix and send through some test messages whilst watching the mail log. If everything goes through fine, without any errors, you can pat yourself on the back and go get a cup of coffee.