ASSP - Anti Spam SMTP Proxy
As an IT consultant, SPAM is an issue, I'm being asked to deal with very often.
SPAM can seriously interfere with the operation of your corporate services,
to say nothing of the effect it may have on any individual's e-mail mail system.
Spammers are, in effect, taking resources away from users and service suppliers
without compensation and without authorization.
There is a few methods of protecting your email from SPAM.
The most common solution is some kind of spam filtering plugin, e.g. Spam Assassin, however it has one very serious issue - performance under heavy load. This solution basically requires to fork a new process for each new email arriving.
It also requires, sometimes tricky, integration with your SMTP server.
It is much more elegant and flexible to use SMTP Spam proxy.
It's like having front-end SMTP server that receives all the emails, blocks SPAM, and passes validated (SPAM free) SMTP sessions to your regular SMTP server for delivery.
One of the benefits of having the SMTP proxy, is that nothing needs to be done to integrate this solution with your existing SMTP server. Your SMTP server is not even aware that anything changed.
If you upgrade or relpace your SMTP server with a different one, you don't need to worry about integration issues; ASSP will work with any SMTP server, be it exim, sendmail or MS Exchange.
One of the SMTP Spam proxies I can recommend is ASSP: http://assp.sourceforge.net
Assuming you will run SMTP proxy and your SMTP server on the same machine (and why not ?), easy to way to set it up, is to change the IP address of your regular SMTP server, so it doesn't open port 25 (SMTP) on the public IP, but listens to all connection on private IP 127.0.0.1.
This way, from the point of view of SMTP clients connecting to your server, nothing has been changed.
Then, you configure ASSP to listen on the public IP (formerly used by your SMTP server), and deliver all emails to 127.0.0.1:25
ASSP has very rich, web based GUI that allows to play around with many configuration settings (and doesn't require any additional components such web server or database server, which seems to be a norm these days. Any kid developing open source software just must use MySQL server, even if it only needs to store lousy 10 bytes of data :).
Check out ASSP Wiki for more details.
In our IT consulting projects, whenever setting up a SMTP server is involved, we usually recommend this, or similar solution. ASSP works very nicely with our favourite email combo: exim/dovecot, and it really is able to filter out at least 95% of spam.
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