A few comments on my article The perfect network server in issue 17 requested some more in depth follow-up pieces. This is what I hope to be the first of those. It focuses on Exim, the mail transfer agent (MTA), specifically setting it up with spam scanning. It is based on setups I currently use, hosted on Debian GNU/Linux.

Dspam filters spam with the best. In my installation, it stops over 98% of all spam: I’ve only had one false positive in the last year, and that was a message to the Dspam list that contained a real spam!

Administering Dspam is a breeze. No rules to configure, new users can automatically benefit from a global dictionary and quarantine management is simple. But getting a Dspam quarantine set up the first time, without losing any email, can challenge the most seasoned mail administrators.

If you are responsible for maintaining an internet-connected mail-server, then you have, no doubt, come to hate spam and the waste of resources which comes with it. When I first decided to lock down my own mail-server, I found many resources that helped in dealing with these unwanted messages. Each of them contained a trick or two, however very few of them were presented in the context of running a real server, and none of them demonstrated an entire filtering framework.

SMTP is an abbreviation for “Simple Mail Transfer Protocol”, and is the standard internet protocol for sending email from one system to another. Although the word “simple” belies the inherent complexity of the protocol, SMTP has proved to be a remarkably robust, useful, and successful standard. The design decisions that made it so useful, though, have given spammers and infectious code an easy way to spread their unwanted messages. Its recent evolution reflects the tug-of-war between those unsavory players and the administrators who want to protect their systems and their users.