E-mail security continues to be a hot-button issue for IT administrators, who now find more moving parts in mail security solutions than they did just a couple of short years ago. Fighting viruses and spam were the original spurs for creating e-mail security appliances, and anti-spam is still the most important component of mail security. But the solutions have evolved to meet a host of additional requirements. These include securing connections between users, both internal and external; preventing loss of corporate data; stopping new types of threats such as phishing, spyware, and other types of malware; and blocking DoS and other network attacks as well as some application-layer attacks on mail servers.

There are three basic types of e-mail security solutions on the market: software-only, appliances, and hosted solutions. Software-only products range from free, such as the open source SpamAssassin, to quite expensive, but there are relatively few software-only solutions, primarily because setting up all the necessary software is complex and easy to get wrong. Thus, most vendors provide an appliance to run their software on, greatly simplifying the installation process. Appliance installation is generally a matter of setting basic network information and telling the appliance where to send e-mail once it's been filtered.

Hosted e-mail security solutions work on a different model. The Internet DNS (domain name service) settings that point to your e-mail server are changed to point to the service instead. The service receives all e-mail sent to your domain and forwards the good stuff to you, filtering out spam and viruses. One advantage to a hosted solution is that the volume of mail coming to your internal network is greatly diminished -- by 80 to 90 percent in most cases. Also, because the bad e-mail is never received at your location, you need not worry about archiving it, which might be an issue if you're doing the filtering in-house.

All the solutions reviewed in this guide are appliances. Services will be added later. Due to the time necessary to allow DNS changes to propagate and other factors involved in testing, it isn't practical to mix testing of appliances with hosted solutions.

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