Linux Firewall Part 6: Overcoming Email Server Problems

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Does the Internet Think You're a Spammer?

As discussed in our article “Why Build a Linux Firewall“, there are many advantages to having a custom-built firewall appliance in your home.  While these Linux distributions are easy to set up and have nice User Interfaces, they still have some problems. Not every feature of Linux is exposed in the GUI, so while these firewalls are very capable they don’t allow for simple customization, which is probably best for the home user.

Sometimes you need to open up an advanced feature here and there, and the need for these expose themselves when you are running an Email server behind your firewall.  One issue that seems to be more common today is the infection of viruses and malware that start broadcasting spam from your network.  If you also run a web-based business, then your business IPs can get blacklisted and your email rejected… all because one of your users made a simple mistake.


Another issue to consider is how your email is sent through the firewall.  Many email servers do an “MX lookup” when they receive mail in an effort to fight spam.  If your mail doesn’t come from the same IP address as your registered MX record, then your mail will likely get dropped.

In this article we show you your options on making your network more secure, and how to preserve your online reputation with a little customization of your Linux firewall.  While we use IPcop (downloadable here), many of these tips work on just about any firewall that uses IPtables.

On the next pages we look at some of these options…