The Tlog - a technology blog

(NOTE: this is part of the “An Anti-Spam gateway” series)

Installing SpamAssassin isn’t too hard, thanks to Perl’s CPAN.

First, type the following:
perl -MCPAN -e shell

If it’s the first time you do that, it will ask you a bunch of questions. Accept the defaults, and when asked about where to download from, try to pick a couple of places near you. When you finally get to the command prompt, it’s time to install the modules.

Now, we could simply tell it to install SpamAssassin, and it would install all the required modules for it. But we’ll want to install some optional ones as well, so, do the following (one at a time, naturally), saying “yes” whenever it asks you if you want to install a pre-requisite (note, also, that some of the modules may already be installed - if so, just move on to the next one):

install MIME::Base64
install DB_File
install Net::DNS
install Net::SMTP
install DBI
install LWP
install Compress::Zlib
install IO::Zlib
install Archive::Tar
install Mail::SpamAssassin


There are 2 still missing, related to MySQL, but we haven’t installed MySQL yet, so… just type quit to exit the CPAN shell.

Onward to Razor, in the next part.

(NOTE: this is part of the “An Anti-Spam gateway” series)

Continuing the Postfix configuration… Edit the /etc/postfix/main.cf file.

Look for, and change according to your configuration, the following options:

myhostname (should be your machine’s name)

myorigin (probably $mydomain)

mynetworks (your network(s), possibly 10.0.0.0/24 in this case)

relay_domains (should be, of course, your domain(s))

bounce_notice_recipient, delay_notice_recipient, error_notice_recipient, policy_notice_recipient (change them all to postmaster@yourdomain, assuming that address exists or is an alias to an existing one - possibly yours, and replacing yourdomain with your domain, of course)

Change the smtpd_client_restrictions option to:
  smtpd_client_restrictions = permit_mynetworks,
   reject_rbl_client relays.ordb.org,
   reject_rbl_client sbl.spamhaus.org,
   permit

Change smtpd_helo_required to yes. Mail servers should learn to behave. Besides, it’s bulk spam senders that normally don’t.

Now, save that file, and edit /etc/postfix/transport. Except for the comments, it should be changed so that it only has this line:

*       smtp:10.0.0.2

(remember? that’s the real mail server’s address)

Leave the editor, then do the following: postmap /etc/postfix/transport, to update the transport.db file.

Now, test it. Yes, when you start it (postfix start), if everything went well, it should already be working as a non-filtering gateway. Assuming, of course, that you configure your firewall so that mail from the outside (to port 25) is delivered there, and that it can connect to the real mail server, and that the latter accepts mail from the gateway.

When it’s working, go to the next part of the series.

(NOTE: this is part of the “An Anti-Spam gateway” series)

“An Anti-Spam gateway” is the Tlog’s third series.

In it, I will write about how to use a Unix-like free operating system such as Linux or OpenBSD, using Postfix, amavisd-new, SpamAssassin with MySQL, and ClamAV to create a free, open source, efficient mail gateway, for tagging spam (I don’t believe in deleting it automatically, that should be up to the users themselves) and stopping email viruses.

While I plan to make this not too advanced, I won’t deal with the basics here, like the installation of the OS, or uncompressing files, and so on.

Also, I won’t explore all the alternatives. This is a HOWTO, not a reference manual. Think of it as a recipe: while a cook is free to change some of the ingredients or procedures, the recipe doesn’t usually say “if you do this instead, that will be the result”. For instance, you may not require an anti-virus, or may want to use a different one, or may want to delete spam messages above a certain score, or may not use MySQL for the Bayes database… all of those possibilities are perfectly fine. I just won’t explore them here.

I hope this series is useful. Few companies, except perhaps multinationals, have gateways as good as this one will be. Trust me. I may be missing out the money I could make by selling “consulting” to companies to do this, instead of just posting the information on the net; however, I don’t want to make a living of installing and configuring email gateways :), and, also, if the majority of companies (and possibly even ISPs) adopt something like this, then there may be, in the future, less spam out there. Making the world a better place, and all that stuff. A guy can dream.