DSL Security on Unix

If you have Linux or any other operating system running the mail server Sendmail, you may inadvertently run across spammers. They're very good at probing networks for systems running mail servers, and if they find you, they'll use your mail server to relay their mail to tens of thousands or even millions of addresses. I'm sure you can imagine the kind of load that will put on your DSL connection. MM Internet probably won't even notice if this happens to you, but you almost certainly will. The solution is easy - upgrade to Sendmail version 8.9.x or above, because those versions prevent relaying. Sendmail included with RedHat 5.2 and below is 8.8 and allows relaying. You can grab the latest sendmail from ftp.sendmail.org.

You may also want to consider QMail, a widely used alternative to sendmail that is considered to be very secure. Most Linux distributions come with a copy of QMail, although it is not generally installed by default.

If you're running Linux, it has firewalling features built into the latest kernels. We recommend the Linux Firewall HOWTO for information about configuring it. We also recommend the more general Linux Security HOWTO. It's a free firewall, so we'd recommend spending the time to learn about it.