Copyright © 2004 The FreeBSD Documentation Project
An article written for the sole purpose of explaining the relaydelay system on a FreeBSD mail server. A relaydelay or greylisting server cuts down on spam simply by issuing a TEMPFAIL error message to every incoming email. The purpose behind this idea is that most spammers use their personal computers with software to do their spamming. A real mail server should queue the message and try to send it later. Thus the spammer most likely moves on to the next host in place of trying to send the email again. This is an excellent idea; at least until the spammers begin to use software that offers to try again. But how does this work exactly? Well, when an email is received the message ID is stored in a database and the TEMPFAIL is returned along with the email. If the email is resent, the message ID will be checked against the message IDs currently stored in the database. If it exists in the database then the email is permitted to reach its intended recipient. Otherwise, the ID will be stored and a TEMPFAIL will be issued. This cycle will repeat with every email which comes into the server. From my personal experience, this really does cut out 90% of the spam.
Install perl using
#pkg install lang/perl5.16
Now for the database server; MySQL is perfect for this sort of work. Install the databases/mysql40-server along with databases/p5-DBD-mysql40. The previous port should imply the installation of databases/p5-DBI-137 so that knocks off another step.
Install the perl based portable
server plugin, net/p5-Net-Daemon
port. Most of these port installations should have
been straight forward. The next step will be more
involved.
Now install the
mail/p5-Sendmail-Milter
port. As of this writing the Makefile
contains a line beginning with BROKEN,
just remove it or comment it out. It is only marked
this way because FreeBSD neither has nor installs
a threaded perl package by default. Once that
line is removed it should build and install perfectly
fine.
Create a directory to hold temporary configuration files:
#mkdir /tmp/relaydelay#cd /tmp/relaydelay
Now that we have a temporary directory to work in, the
following URLs should be sent to the
fetch command:
#fetch http://projects.puremagic.com/greylisting/releases/relaydelay-0.04.tgz#fetch http://lists.puremagic.com/pipermail/greylist-users/attachments/20030904/b8dafed9/relaydelay-0.04.bin
The source code should now be unpacked:
#gunzip -c relaydelay-0.04.tgz | tar xvf -
There should now be several files into the temporary directory
by this point. The appropriate information can now be passed to
the database server by importing it from the
mysql.sql file:
#mysql < relaydelay-0.04/mysql.sql
And patch the other files with the
relaydelay.bin by running:
#patch -d /tmp/relaydelay/relaydelay-0.04 < relaydelay.bin
Edit the relaydelay.conf and the
db_maintenance.pl file to append the
correct username and password for the
MySQL database. If the database was
built and installed like the above then no users or passwords
exist. This should be altered before putting this into
production, that is covered in the database documentation and
is beyond the scope of this document.
Change the working directory to the
relaydelay-0.04
directory:
#cd relaydelay-0.04
Copy or move the configuration files to their respective directories:
#mv db_maintenance.pl relaydelay.pl /usr/local/sbin#mv relaydelay.conf /etc/mail#mv relaydelay.sh /usr/local/etc/rc.d/
Test the current configuration by running:
#sh /usr/local/etc/rc.d/relaydelay.sh start
This file will not exist if the previous mv(1) commands were neglected.
If everything worked correctly a new file,
relaydelay.log, should exist in
/var/log. It should
contain something similar to the following text:
Loaded Config File: /etc/mail/relaydelay.conf Using connection 'local:/var/run/relaydelay.sock' for filter relaydelay DBI Connecting to DBI:mysql:database=relaydelay:host=localhost:port=3306 Spawned relaydelay daemon process 38277. Starting Sendmail::Milter 0.18 engine.
If this does not appear then something went wrong, review
the screen output or look for anything new in the
messages log file.
Glue everything together by adding the following line to
/etc/mail/sendmail.mc or the customized
site specific mc file:
INPUT_MAIL_FILTER(`relaydelay', `S=local:/var/run/relaydelay.sock, T=S:1m;R:2m;E:3m')dnl
Rebuild and reinstall the files in the
/etc/mail directory and restart
sendmail. A quick make
restart should do the trick.
Obtain the perl script located at
http://lists.puremagic.com/pipermail/greylist-users/2003-November/000327.html
and save it in the
relaydelay-0.04
directory. In the following examples this script is
referred to as addlist.pl.
Edit the whitelist_ip.txt file and
modify it to include IP addresses of servers
which should have the explicit abilities to bypass the
relaydelay filters. i.e., domains
from which email will not be issued a
TEMPFAIL when received.
Some examples could include:
192.168. # My internal network. 66.218.66 # Yahoo groups has unique senders.
The blacklist_ip.txt file should
be treated similarly but with reversed rules. List within
this file IPs which should be denied without
being issued a TEMPFAIL. This list of
domains will never have the opportunity to prove that they are
legitimate email servers.
These files should now be imported into the database with
the addlist.pl script obtained a few
lines ago:
#perl addlist.pl -whitelist 9999-12-31 23:59:59 < whitelist_ip.txt#perl addlist.pl -blacklist 9999-12-31 23:59:59 < blacklist_ip.txt
To have relaydelay start with
every system boot, add the
relaydelay_enable="YES" to the
/etc/rc.conf file.
The /var/log/relaydelay.log log file
should slowly fill up with success stories. Lines like the
following should appear after a short time, depending on how
busy the mail server is.
=== 2004-05-24 21:03:22 === Stored Sender: <[email protected]> Passed Recipient: <[email protected]> Relay: example.net [XXX.XX.XXX.XX] - If_Addr: MY_IP_ADDRESS RelayIP: XX.XX.XX.XX - RelayName: example.net - RelayIdent: - PossiblyForged: 0 From: [email protected] - To: local_user InMailer: esmtp - OutMailer: local - QueueID: i4P13Lo6000701111 Email is known but block has not expired. Issuing a tempfail. rowid: 51 IN ABORT CALLBACK - PrivData: 0<[email protected]>
The following line may now be added to
/etc/newsyslog.conf to cause for
relaydelay.log rotation at every
100 Kb:
/var/log/relaydelay.log 644 3 100 * Z
At some point there was an error about improper
perl variables in the
/etc/mail/relaydelay.conf. If those
two variables are commented out then configuration may
proceed as normal. Just remember to uncomment them before
starting the relaydelay process.